A filler in plastics is a solid particulate additive, almost always a mineral, that is compounded into the polymer at 5 to 70 wt% of the compound, either to replace resin volume or to add a property the polymer does not have, and 13 types carry that job across the industry. Fillers are the second-largest additive group by weight, at 28 % of global additive consumption (Ceresana, 2023), so which mineral belongs in which polymer, and at what level?
Fillers do two jobs. Extender fillers, such as ground calcium carbonate, ground limestone and dolomite, displace resin volume at the lowest cost per litre; across all industries more than 53 million tonnes a year is consumed, worth about USD 18 billion from more than 700 producers. Functional fillers, such as boron nitride, barium sulfate and hollow glass microspheres, buy a property the polymer cannot reach. The two jobs move 6 levers: stiffness, heat deflection temperature, density, dimensional stability, conductivity and cost.
Fillers are one of the 43 families of plastic additives, and this reference covers what separates a filler from a reinforcement, the 4 mechanisms by which a particle changes a polymer, the 13 types with their density, hardness and aspect ratio, the loading each polymer takes, surface treatment, selection, testing, the EU and US regulatory position, and who sells the minerals.
Table 1. The 13 fillers for plastics at a glance. The Page column carries the one link to each type on this page.
| # | Filler | Group | Shape and aspect ratio | Typical job | Page |
|---|---|---|---|---|---|
| 1 | Calcium carbonate | Carbonate | Blocky, AR 1-3 | Cheapest volume extender, opacity, HCl scavenging in PVC | GCC, PCC, coated grades and breathable film are on calcium carbonate in plastics |
| 2 | Talc | Platy silicate | Platy, AR 5-40 | Stiffness and heat deflection in polypropylene, nucleation | T10 to T40 grades and the nucleation effect are on talc in plastics |
| 3 | Kaolin | Platy silicate | Platy, AR 10-30 | Extender, surface finish, electrical insulation when calcined | Hydrous versus calcined grades are on kaolin in plastics |
| 4 | Mica | Platy silicate | Platy, AR 20-100 | Low warpage, stiffness and barrier in engineering plastics | Muscovite, phlogopite and synthetic grades are on mica in plastics |
| 5 | Wollastonite | Acicular silicate | Acicular, AR 5-30 | Strength and heat deflection without fibre warpage | Acicular and surface-treated grades are on wollastonite in plastics |
| 6 | Barium sulfate | Sulfate | See the page | Density, sound damping and radiopacity | Barite, blanc fixe and radiopaque use are on barium sulfate in plastics |
| 7 | Synthetic amorphous silica | Silica | Aggregated nano primaries, 1-100 nm | Rheology control, matting, reinforcement of silicone | Fumed, precipitated and crystalline silica are separated on silica in plastics |
| 8 | Diatomaceous earth | Silica | Porous disc, AR 2-10 | Film antiblock at ppm level | Grades, top cut and the crystalline-silica caveat are on diatomaceous earth |
| 9 | Hollow glass microspheres | Low-density | Sphere, 10-300 µm | Density reduction | Crush strength and density reduction are on glass microspheres in plastics |
| 10 | Nanoclay | Nano | Platelet about 1 nm thick; halloysite tube AR 5-20 | Stiffness, heat deflection and gas barrier at a few wt% | Exfoliation and the two food-contact entries are on nanoclay (organoclay) in plastics |
| 11 | Thermally conductive ceramics | Ceramic | Platy (h-BN) to blocky (alumina) | Heat transfer without electrical conduction | Boron nitride, aluminium nitride and alumina are compared on thermally conductive fillers |
| 12 | Carbon fillers | Carbon | Platy (graphite) to tubular (CNT) | Electrical and thermal conduction, lubricity | Percolation data and the 2026 classification are on carbon nanotubes (CNT) in plastics |
| 13 | Wood flour and cellulose | Organic | Irregular fibrous particle | Bulk and wood character in WPC decking and profile | WPC formulations are on wood flour and cellulose fillers |
Aspect ratio and shape come from our source library reference table, cross-checked against PubChem.
What Is a Filler in Plastics?#
A filler is a solid particulate additive dispersed in a polymer matrix at comparatively high loading, usually 5 to 70 wt% of the compound, to lower cost or to change stiffness, density, heat resistance, conductivity, opacity or barrier. Across finished plastic products the filler fraction runs from 0 to 50 wt%, while reinforcements sit in a narrower 15 to 30 wt% band, a range published by Chea and co-workers in 2025 and adapted from the additive inventory of Hahladakis and colleagues in 2018. The particle is chemically inert: it does not scavenge radicals, absorb ultraviolet light or release water.
Which mineral powders in a plastic are therefore not fillers? Four groups are excluded by function: pigments, including titanium dioxide, carbon black and the iron oxides, bought to colour and opacify; mineral flame retardants, aluminium trihydrate and magnesium dihydroxide, bought because they release water endothermically; reinforcing fibres, glass, carbon, aramid and basalt, which work by a different load-transfer mechanism; and blowing agents, which create gas rather than occupy volume. The boundary matters administratively too: the European Chemicals Agency excluded fillers and lubricants from its Plastic Additives Initiative mapping because too few REACH registrations reported use in plastic articles, so its 418-row additive list contains no filler rows.
Why are fillers added to plastics?#
Fillers are added to plastics for 6 reasons: to replace resin volume with a cheaper mineral, to raise stiffness and heat deflection temperature, to hold a moulded part dimensionally stable, to move the density up or down, to add a function such as thermal conductivity or radiopacity, and to shorten the cooling part of the moulding cycle. The 6 reasons are set out below with the mineral bought for each.
- Cost per litre. Ground calcium carbonate is the cheapest mineral that disperses well, and Omya states that it can replace up to 60 % of the polymer in finished articles.
- Stiffness and heat resistance. Talc is dosed at 10 to 40 wt% in polypropylene for modulus and heat deflection temperature.
- Dimensional stability. Mica and wollastonite hold a moulded part flat because neither shrinks the way a unidirectional short fibre does.
- Density, upwards. Barium sulfate is used at up to 70 % in polypropylene and polystyrene for weight, sound damping or X-ray contrast.
- Density, downwards. Cenospheres, the hollow fly-ash particle, sit at 0.4 to 0.8 g/cm3, below every common thermoplastic.
- Cycle time. Omya reports that calcium-carbonate-filled polymers transfer heat more quickly, which increases line speed.
Loadings differ by an order of magnitude between those 6 jobs.
Filler or reinforcement: what is the difference?#
A reinforcement is a filler whose aspect ratio and interface are high enough to carry mechanical load, so it raises tensile strength as well as stiffness, while a plain filler raises stiffness but usually lowers strength. The criterion is the particle's geometry and its bond to the matrix, not its chemistry or its price. Aspect ratio separates the candidates cleanly: calcium carbonate sits at 1 to 3, kaolin at 10 to 30, talc at 5 to 40, wollastonite at 5 to 30 and mica at 20 to 100, while an exfoliated nanoclay platelet reaches far higher values. For the definition of the ratio itself, see aspect ratio.
Load transfer is the mechanism behind the definition. Fibre reinforcement was explained by H.L. Cox in 1952 with the shear-lag model, and A. Kelly and W.R. Tyson added the critical fibre length in 1965, lc = sigma_f x d / (2 x tau), below which a fibre pulls out instead of breaking. Stress passes into the particle through interfacial shear, which is why glass fibre carries a sizing of 0.5 to 2.0 wt% of the fibre. Glass, carbon, basalt and natural fibres are covered on reinforcing fibers for plastics, and reinforcements concentrate at 15 to 30 wt% of the product while fillers spread from 0 to 50 wt%.
Is a filler the same as an extender?#
An extender is one kind of filler, not a synonym: extender fillers such as ground calcium carbonate are chosen to displace resin, while functional fillers such as boron nitride or barium sulfate are chosen for a property the polymer cannot reach on its own. The functional list is the longer one: aluminium trihydrate and magnesium dihydroxide for fire performance, boron nitride and aluminium nitride for heat transfer, barium sulfate for density and radiopacity, nanoclay for gas barrier, talc for nucleation, and hollow glass microspheres for low density. One mineral can play both parts: ground calcium carbonate is an extender in a pipe compound and a functional particle in breathable film.
How Do Fillers Change the Properties of a Plastic?#
Fillers change a plastic through 4 mechanisms: they occupy volume the polymer no longer has to fill, they stiffen it in proportion to their volume fraction and aspect ratio, they either bond to the matrix or debond from it under load, and they change how fast the compound heats, cools and flows. Modulus follows the first two, modelled by the equations of J.C. Halpin and J.L. Kardos in Polymer Engineering and Science in 1976. Strength follows the third, quantified by the interaction parameter B that B. Pukanszky introduced in Composites in 1990, with the review by Fu, Feng, Lauke and Mai in Composites Part B in 2008 as the canonical synthesis. The four numbers on a supplier datasheet, particle size, aspect ratio, surface area and oil absorption, are explained on filler properties: particle size, aspect ratio and oil absorption.
Stiffness and heat deflection: why aspect ratio decides#
Stiffness rises with the volume fraction of filler and with its aspect ratio, which is why 20 wt% of platy talc stiffens polypropylene far more than 20 wt% of blocky calcium carbonate. The standard model is the pair of equations published by J.C. Halpin and J.L. Kardos in Polymer Engineering and Science in 1976, in which the reinforcing efficiency of an aligned platelet or fibre enters through a shape factor of roughly twice the aspect ratio. A particle with an aspect ratio of 1 contributes almost nothing beyond its own volume; one with an aspect ratio of 30 contributes a shape factor an order of magnitude larger.
Heat deflection temperature moves with the same lever, because it is read at a fixed deflection under load and tracks modulus. The most-cited demonstration is a nanocomposite rather than a mineral loading: Kojima, Usuki, Kawasumi and Okada at Toyota Central R&D Labs reported in the Journal of Materials Research in 1993 that 4.7 wt% of montmorillonite in nylon 6 raised the heat deflection temperature to 152 °C, 87 °C above neat nylon 6, with strength and modulus up and impact comparable. That result is why aspect ratio, not loading, is the first question in a stiffness problem.
Strength, impact and the filler-polymer interface#
Whether a filler raises or lowers tensile strength depends on the interface: a poorly bonded blocky particle acts as a void and lowers strength, while a coupled high-aspect-ratio particle transfers load and raises it. Pukanszky's interaction parameter B, published in Composites in 1990, puts a number on that interface, and the 2008 review by Fu, Feng, Lauke and Mai traces how particle size, volume fraction and adhesion together set composite strength.
Impact behaves less predictably, and the exception is commercially important. Thio, Argon, Cohen and Weinberg at MIT reported in Polymer in 2002, and Zuiderduin, Westzaan, Huetink and Gaymans at the University of Twente in Polymer in 2003, that fine, well-dispersed, stearic-acid-coated calcium carbonate below about 3 µm can toughen polypropylene: the particles debond under load, the matrix ligaments between the voids yield, and notched impact strength rises rather than falls. The condition is dispersion. Agglomerates and the coarse tail of the distribution, the d98 top cut, act as crack initiators, which is why the top cut matters more than the d50 for impact strength and film pinholes. For the definitions behind those numbers, see particle size (D50 and top cut).
Density, shrinkage, warpage and cycle time#
Every filler changes the density of the compound, because minerals are 2 to 4.5 times denser than the polymer they replace, and that single fact drives part weight, cost per litre and whether the compound still floats in a recycling plant. The densities that set the arithmetic run from amorphous silica at 2.2 and kaolin at 2.6 through calcium carbonate at 2.7 to 2.95 and wollastonite at 2.8 to 2.9 to alumina at 3.97 and barium sulfate at 4.25 to 4.5 g/cm3. The 3 dimensional consequences are listed below.
- Density upwards. Barium sulfate at 4.25 to 4.5 g/cm3 raises compound density fastest, which is the point in sound-damping and radiopaque parts.
- Density downwards. Only two particle classes push density down: hollow glass microspheres, and cenospheres at 0.4 to 0.8 g/cm3. Fumed silica has a bulk density of 160 to 190 kg/m3, but that is powder bulk density, not the density it contributes in a compound.
- Shrinkage and warpage. Talc, mica, glass beads and wollastonite are the low-warpage choices, because none is a unidirectional fibre that shrinks differently along and across the flow direction.
Cycle time moves with thermal transport rather than mechanics. Omya reports that calcium-carbonate-filled polymers transfer heat more quickly and so increase line speed, and talc nucleates the alpha form of polypropylene, which shortens the time the part needs in the mold.
What fillers cost you: melt viscosity, machine wear and stabilizer demand#
A filler is never free: it raises melt viscosity, it abrades screws, barrels and gates in proportion to its Mohs hardness, and some minerals consume part of the stabilizer package. The 3 costs are set out below with the mineral property that governs each.
- Melt viscosity. Specific surface area drives coupling-agent demand and melt viscosity, so a fumed silica at 50 to 600 m2/g thickens a melt at a fraction of the loading a ground mineral needs.
- Machine wear. Abrasion scales with Mohs hardness: talc 1, kaolin 2, calcium carbonate 3 to 4, barium sulfate 3.3, wollastonite 4.5 to 5, silica and diatomaceous earth 5.5 to 6, and alumina about 9.
- Stabilizer demand. Talc carries Lewis-acid surface sites that can catalyse polymer oxidation and depolymerization at elevated temperature, so a talc-filled polypropylene needs a stronger antioxidant package than the unfilled resin. Acidic kaolins and silanol-rich silicas adsorb phenolic antioxidants and hindered amine light stabilizers directly.
Stabilizer demand is a formulation cost, recovered by raising the dose or changing the chemistry of the antioxidants for plastics in the package. One further number belongs in the cost column: oil absorption, measured to ISO 787-5 or ASTM D281, is the proxy for how much plasticizer a filler takes out of a flexible PVC compound.
13 Types of Fillers for Plastics#
The 13 types of fillers used in plastics are calcium carbonate, talc, kaolin, mica, wollastonite, barium sulfate, synthetic amorphous silica, diatomaceous earth, hollow glass microspheres, nanoclay, thermally conductive ceramics, carbon fillers and wood flour. The order follows chemistry and plastics-relevant tonnage: the carbonate first, then the three platy silicates, the acicular silicate, the sulfate, the two silicas, the low-density and nano classes, the ceramics and carbons, and the one organic filler with real volume. Each type gives what the particle is, how it works, the level it is used at and one regulatory or market fact.
1. Calcium carbonate (GCC, PCC and dolomite)#
Calcium carbonate is the cheapest and by far the most used filler in plastics, a blocky particle with an aspect ratio of 1 to 3 that replaces resin volume in PVC, polypropylene and polyethylene at 5 to 70 phr. It reaches the compound in three forms: ground calcium carbonate (GCC), milled from limestone, marble or chalk; precipitated calcium carbonate (PCC), manufactured by carbonating lime; and dolomite, CaMg(CO3)2, CAS 16389-88-1, at a density of 2.85 g/cm3 and Mohs 3.5 to 4. Calcite has a density of 2.7 to 2.95 g/cm3, Mohs 3 to 4 and a mean particle size of 0.02 to 30 µm.
Calcium carbonate is CAS 471-34-1, molecular weight 100.09, and it carries EU 10/2011 entry FCM 21 as a salt of carbonic acid plus 21 CFR 184.1191 (GRAS). The two grades differ under REACH: GCC is exempt under Annex V, while PCC is registered, with 296 active dossiers. Two functions go beyond volume: fine GCC nucleates the pores of breathable microporous film during biaxial stretching, and calcium carbonate neutralises the hydrogen chloride that PVC releases. Typical loadings run 15 to 20 % in a uPVC drainpipe, 5 to 15 % coated in a window profile, up to 70 phr in a PVC cable compound and 20 to 40 % in polypropylene.
2. Talc#
Talc is a platy magnesium silicate with an aspect ratio of 5 to 40 and a Mohs hardness of 1, the softest mineral there is, and it is the standard stiffness filler for automotive polypropylene at 10 to 40 wt%. Its formula is Mg3Si4O10(OH)2, CAS 14807-96-6, molecular weight 379.27, with a density of 2.7 to 2.8 g/cm3 and a mean particle size of 0.5 to 20 µm. The same platelet does a second job at a lower dose: 0.5 to 5 wt% has been studied as a nucleating agent in polypropylene, and 6 wt% is used in PLA.
Talc holds EU 10/2011 entry FCM 615 and the US routes 21 CFR 178.3297 and 182.90, with 15 active REACH dossiers. Plastics take 32 % of US talc sales, against world mine production of 6.9 million tonnes led by China and India at 1.4 Mt each, the United States at 0.53 Mt and Brazil at 0.48 Mt (USGS, 2024). The classification file is open: the Risk Assessment Committee opinion adopted on 20 September 2024 recommends Carc. 1B H350 and STOT RE 1 H372, a proposal and not an entry in Annex VI to Regulation (EC) No 1272/2008, and the International Agency for Research on Cancer placed asbestos-free talc in Group 2A in July 2024.
3. Kaolin (hydrous and calcined)#
Kaolin is a platy hydrous aluminium silicate, china clay, used in plastics mainly in its calcined form, which is fired above about 400 °C to drive off the structural water and give a harder, whiter, electrically insulating particle. Hydrous kaolin is CAS 1332-58-7, EC 310-194-1, with a density of 2.6 g/cm3, Mohs 2, a mean size of 0.2 to 8 µm and an aspect ratio of 10 to 30; calcination is irreversible and produces a separate substance, CAS 92704-41-1, EC 296-473-8, with 4 active REACH dossiers.
The two identities carry two food-contact entries under Regulation (EU) No 10/2011: FCM 410 for kaolin, which permits particles thinner than 100 nm only below 12 % w/w in an EVOH inner layer behind a functional barrier, and FCM 753 for calcined kaolin; the Annex II aluminium limit of 1 mg/kg applies to the article. In the United States kaolin is GRAS for paper under 21 CFR 186.1256 and appears in 178.3297 as aluminum silicate (China clay). The application that pays for calcined kaolin is wire insulation, where it raises the volume resistivity of PVC. World kaolin production is 44 million tonnes, 54 % of US sales go to fillers, extenders and binders, and the US unit value is USD 160 per tonne (USGS, 2024).
4. Mica#
Mica has the highest aspect ratio of the mineral fillers, 20 to 100, which is why it is the mineral of choice when a moulded part has to stay flat and stiff, for example in mineral-reinforced polyamide and in PC/ABS. It is CAS 12001-26-2, EC 601-648-2, with a density of 2.6 to 3.2 g/cm3, a Mohs hardness of 2.5 to 4 and a mean particle size spanning 5 to 1,000 µm, and it is supplied as muscovite, phlogopite or synthetic fluorophlogopite.
Mica is authorised under EU 10/2011 as FCM 597 with no specific migration limit, and in the United States it appears in 21 CFR 178.3297 as aluminum and potassium silicate, in 177.2600 as a rubber filler and in 177.2410 as a phenolic adjuvant. World scrap and flake mica production is 380,000 tonnes (USGS, 2024).
5. Wollastonite#
Wollastonite is a needle-shaped calcium silicate with an aspect ratio of 5 to 30, the only common mineral filler that behaves partly like a short fibre, so it raises strength and heat deflection temperature without the warpage of glass fibre. It is CAS 13983-17-0, with a density of 2.8 to 2.9 g/cm3, Mohs 4.5 to 5, a mean size of 1 to 500 µm, an aqueous slurry pH of 8 to 10 and a composition of 48.3 % CaO and 51.7 % SiO2 when pure. That alkaline pH decides which silane couples to the surface.
It is authorised in food contact as FCM 613 with no specific migration limit, carries no REACH dossier as an unmodified natural mineral under Annex V, and was placed in Group 3 by the International Agency for Research on Cancer in Monograph volume 68 in 1997. World production outside the United States is 1.1 million tonnes, led by China at 800,000 tonnes, India at 120,000 tonnes and Mexico at 95,000 tonnes; plastics and rubber took 25 to 35 % of US sales in 2009 (USGS, 2024).
6. Barium sulfate#
Barium sulfate is the density filler: at 4.25 to 4.5 g/cm3 it is the heaviest of the common minerals, and it is chosen when a part has to feel solid, damp sound or show up on an X-ray. It is CAS 7727-43-7, with Mohs 3.3 and a water solubility of 0.00031 g per 100 g at 20 °C, which is why the barium in it does not migrate the way a soluble barium salt would. It is supplied as natural barite and as precipitated blanc fixe, and it is used at up to 70 % in polypropylene and polystyrene.
The regulatory position of barium sulphate is unusual: it has no named entry on the Union list of Regulation (EU) No 10/2011 and is permitted under Article 6(3)(a) as a salt of the authorised sulphuric acid, FCM 511, subject to the Annex II barium limit of 1 mg/kg. Barite world production is 8.2 million tonnes, more than 90 % of US consumption goes to drilling mud, and the US ground unit value is USD 220 per tonne (USGS, 2024).
7. Synthetic amorphous silica (fumed and precipitated)#
Synthetic amorphous silica is the highest-surface-area filler in plastics, at 5 to 600 m2/g, and it is used less to fill volume than to control rheology, matt a surface or reinforce a silicone. It is CAS 7631-86-9, with 371 active REACH dossiers, and its EU 10/2011 entry FCM 504 carries an explicit nanoform specification: primary particles of 1 to 100 nm aggregated to 0.1 to 1 µm. Silanated silica has its own entry, FCM 87, and the US routes are 21 CFR 172.480, 178.3297, 177.2600 and 182.90.
The two industrial grades behave differently. Fumed silica, made by flame pyrolysis of silicon tetrachloride, has primary particles of 5 to 50 nm, a surface area of 50 to 600 m2/g and a bulk density of only 160 to 190 kg/m3, and it thixotropes unsaturated polyester and epoxy and reinforces silicone rubber. Precipitated silica has a surface area of 5 to 100 m2/g, agglomerates of 1 to 40 µm and a density of 1.9 to 2.1 g/cm3, and it reinforces rubber and thermoplastic elastomers and serves as an antiblock and matting agent. Two housekeeping points prevent errors: CAS 112945-52-5 and 112926-00-8 are former numbers only, and crystalline silica is separately regulated, cristobalite at FCM 614 and quartz at FCM 616.
8. Diatomaceous earth#
Diatomaceous earth is fossil diatom silica, a porous irregular disc that is used in plastics mostly as a film antiblock at 2,500 to 10,000 ppm, where its rough surface stops film layers welding together. Its composition is 80 to 90 % silica with 2 to 4 % alumina and 0.5 to 2 % iron oxide; filler grades have a mean size of 4 to 30 µm, Mohs 5.5 to 6, an aspect ratio of 2 to 10 and a density of 2 to 2.5 g/cm3. Its refractive index sits close to polyethylene, which keeps film haze low.
Two identities exist and both are authorised in food contact: natural diatomite, CAS 61790-53-2, at FCM 707, and soda-ash flux-calcined diatomite, CAS 68855-54-9, at FCM 734. Three cautions belong with it: the top cut can reach 44 µm against a 25 µm film, the iron content can accelerate degradation, and calcined grades contain crystalline silica and bring respirable silica limits into the plant. World diatomite production is 3.0 million tonnes and the US average price is USD 590 per tonne, with filtration grade at about USD 790 per tonne (USGS, 2024).
9. Hollow glass microspheres#
Hollow glass microspheres are the only filler that makes a compound lighter instead of heavier, thin-walled glass bubbles of 10 to 300 µm that trade stiffness and cost against part weight. Glass microspheres in general span 1 to 1,000 µm. Their weakness is mechanical rather than chemical: up to 80 % of the spheres can break in standard mixing and dispensing equipment, so the survival rate, not the nominal density, decides what the compound weighs.
The food-contact position is simple: glass microballs are authorised under Regulation (EU) No 10/2011 as FCM 39 with no specific migration limit. The fly-ash alternative, cenospheres, reaches 0.4 to 0.8 g/cm3 at a lower price but with wider variation in wall thickness and chemistry.
10. Nanoclay (organoclay and halloysite)#
Nanoclay is layered silicate, usually montmorillonite, whose roughly 1 nm platelets are surface-modified with a quaternary ammonium salt so the polymer can push them apart, and at a few weight per cent it raises stiffness, heat deflection temperature and gas barrier. Montmorillonite is CAS 1318-93-0 and carries no REACH dossier under that natural identity because Annex V exempts it; bentonite is authorised in food contact as FCM 393. A nanofiller has at least one dimension below 100 nm, which for an exfoliated clay is the platelet thickness, and the benchmark result remains the Toyota nylon 6-clay hybrid of 1993.
Food contact is where nanoclay becomes complicated. Article 9(2) of Regulation (EU) No 10/2011 permits a nanoform only when it is explicitly authorised in Annex I, and two organoclay entries exist: FCM 1030, dimethyldialkyl(C16-C18)ammonium-modified montmorillonite, at most 12 % w/w in polyolefins for dry foods at room temperature or below, with the sum of 1-chlorohexadecane and 1-chlorooctadecane at most 0.05 mg/kg; and FCM 1075, hexadecyltrimethylammonium-bromide-modified montmorillonite, at most 4.0 % w/w in PLA for water storage. Both require the platelets to be oriented parallel to the surface and fully embedded. Halloysite is the tubular alternative, at a density of 2.54 g/cm3, an aspect ratio of 5 to 20 and a surface area up to 117 m2/g.
11. Thermally conductive ceramics (boron nitride, aluminium nitride, alumina)#
Thermally conductive ceramics are the fillers used when a plastic part has to move heat but must not conduct electricity, and the three that matter are hexagonal boron nitride, aluminium nitride and alumina. Hexagonal boron nitride, CAS 10043-11-5, is strongly anisotropic, with conductivity far higher in the plane of its platelet than across it; atomically thin boron nitride reaches 751 W/(m·K). Aluminium nitride, CAS 24304-00-5, conducts 70 to 210 W/(m·K) as a polycrystalline powder and up to 285 W/(m·K) as a single crystal, with a coefficient of thermal expansion of 4.2 to 5.3 x 10^-6 per K. Aluminum oxide, CAS 1344-28-1, is the cheap workhorse at 3.97 g/cm3 and a melting point of 2054 °C, but Mohs of about 9 makes it the most abrasive filler here. Fused silica, for comparison, conducts only 1.37 W/(m·K).
The food-contact positions differ sharply. Boron nitride is authorised as FCM 583 under group restriction 16, with a total specific migration limit of 6 mg/kg as boron; alumina is authorised as FCM 418 with the Annex II aluminium limit of 1 mg/kg; aluminium nitride is not listed in Annex I to Regulation (EU) No 10/2011 at all, which rules it out of EU food-contact plastics. Boron nitride has a second use: at 0.005 to 0.5 % it works as a PFAS-free melt-fracture processing aid.
12. Carbon fillers (graphite, carbon nanotubes, graphene)#
Carbon fillers are the conductive family: graphite for heat and lubricity, carbon nanotubes for electrical percolation at a fraction of a per cent, and graphene nanoplatelets for a mix of conductivity, barrier and stiffness. Graphite is CAS 7782-42-5, with 146 active REACH dossiers, and it is thermally and electrically conductive and a solid lubricant. Multi-walled carbon nanotubes reach electrical percolation in polypropylene at reported levels from 0.06 to 0.08 wt% in a co-continuous PP/PS blend after thermal treatment, up to 0.5 to 1.4 wt% in plain polypropylene, and attenuation above 40 dB has been reported for shielding at 10 % nanotube content. Commercial masterbatches carry 10 to 20 wt%. Graphene is CAS 1034343-98-0, with 9 active dossiers.
Regulation separates graphite from the two nanocarbons. Graphite is authorised in food contact as FCM 521; neither carbon nanotubes nor graphene has an entry in Annex I to Regulation (EU) No 10/2011, so under Article 9(2) they cannot be used in EU food-contact plastics. Carbon nanotubes also carry a harmonised classification: index 006-104-00-2, covering multi-walled carbon tubes of 30 nm to 3 µm diameter, at least 5 µm length and an aspect ratio above 3:1, is Carc. 1B H350i and STOT RE 1 H372 (lung, inhalation) under Commission Delegated Regulation (EU) 2024/2564, in application from 1 May 2026.
13. Wood flour and cellulose fibres#
Wood flour is the one organic filler with real volume in plastics, milled sawdust compounded into polyethylene, polypropylene or PVC at loadings that can exceed half the compound to make wood-plastic composite decking and profile. A published recycled-HDPE profile formulation is 34 % rHDPE and 60 % sawdust, with a coupling wax, stearic acid and pigment as the balance. The processing window is the constraint: a wood-plastic composite runs about 28 °C below the unfilled resin, because cellulose and lignin scorch.
Adhesion is the second constraint, since the cellulose surface is polar and a polyolefin is not, so wood flour and natural fibres need a maleated polyolefin coupling agent to bond at all. In food contact, cellulose is authorised under Regulation (EU) No 10/2011 as FCM 553, both as an additive and as a monomer, while lignocellulose, FCM 595, is authorised only as a monomer or starting substance, a distinction that catches formulators who assume the two entries are interchangeable.
Plastic Fillers Compared: Density, Hardness, Aspect Ratio and What Each One Changes#
The comparison below puts all 13 fillers side by side with the four numbers that decide a formulation: density, Mohs hardness, aspect ratio and typical particle size. Every value repeats a figure stated above; where no value is established, the cell reads "see page" rather than an estimate.
Table 2. The 13 plastic fillers compared.
| # | Filler | Density (g/cm3) | Mohs | Aspect ratio and shape | Mean particle size (µm) | Raises | Lowers | Typical level |
|---|---|---|---|---|---|---|---|---|
| 1 | Calcium carbonate | 2.7-2.95 | 3-4 | 1-3, blocky | 0.02-30 | Stiffness, opacity, density, line speed | Cost per kg, tensile strength when uncoated | 5-70 phr depending on polymer |
| 2 | Talc | 2.7-2.8 | 1 | 5-40, platy | 0.5-20 | Stiffness, heat deflection, nucleation rate | Impact strength, antioxidant reserve | 10-40 wt% in PP |
| 3 | Kaolin | 2.6 | 2 | 10-30, platy | 0.2-8 | Volume resistivity (calcined), surface finish | Cost per kg | See the page |
| 4 | Mica | 2.6-3.2 | 2.5-4 | 20-100, platy | 5-1,000 | Stiffness, dimensional stability, barrier | Warpage, impact strength | See the page |
| 5 | Wollastonite | 2.8-2.9 | 4.5-5 | 5-30, acicular | 1-500 | Strength, heat deflection | Warpage | See the page |
| 6 | Barium sulfate | 4.25-4.5 | 3.3 | See the page | See the page | Density, sound damping, radiopacity | Cost per litre | Up to 70 % in PP and PS |
| 7 | Synthetic amorphous silica | 2.2 (amorphous) | 5.5 | Aggregated nano primaries | 0.1-1 (aggregates); 1-40 (precipitated agglomerates) | Melt viscosity, thixotropy, matting | Gloss, flow | See the page |
| 8 | Diatomaceous earth | 2-2.5 | 5.5-6 | 2-10, porous disc | 4-30 | Antiblock efficiency, surface roughness | Blocking force, film clarity margin | 2,500-10,000 ppm in PE film |
| 9 | Hollow glass microspheres | See the page | See the page | About 1, hollow sphere | 10-300 (diameter) | Buoyancy, weight saving | Density, impact strength | See the page |
| 10 | Nanoclay | See the page (halloysite 2.54) | See the page (halloysite 2.5) | Platelet about 1 nm thick; halloysite tube 5-20 | 1-20 (halloysite) | Stiffness, heat deflection, gas barrier | Permeability | 4.7 wt% in the nylon 6-clay hybrid; at most 12 % w/w under FCM 1030 |
| 11 | Thermally conductive ceramics | Alumina 3.97 | Alumina about 9 | h-BN platy, alumina blocky | See the page | Thermal conductivity | Electrical conductivity stays low | See the page |
| 12 | Carbon fillers | See the page | See the page | Graphite platy; MWCNT aspect ratio above 3:1 | See the page | Electrical and thermal conductivity, lubricity | Volume resistivity | MWCNT 0.06-1.4 wt% reported in PP |
| 13 | Wood flour and cellulose | See the page | See the page | Irregular fibrous particle | See the page | Bulk, wood character, stiffness | Processing temperature, moisture resistance | About 60 % in an rHDPE profile |
Density, hardness, aspect ratio and size come from our source library (PubChem and the published filler property table); loading figures are the sourced formulations cited in this article. Aspect ratio is indicative: a supplier grade can sit outside the range.
How Much Filler Can a Plastic Take? Loading Levels by Polymer and Application#
Filler loading in a plastic product runs from a few hundred parts per million for a film antiblock to about 50 wt% for a mineral-filled compound, and it is written three ways: wt% for most thermoplastics, vol% when the argument is mechanical, and phr for PVC and rubber. The three units are not interchangeable. Volume fraction governs the mechanics, because modulus and percolation depend on the space the particle occupies; weight fraction governs cost and density; and parts per hundred resin is the PVC and rubber convention, converted with wt% = phr of the ingredient divided by total phr, times 100. Conversion between phr, wt% and vol% is worked through on PHR (parts per hundred resin). One warning follows from the density table: 30 wt% of barium sulfate is a far smaller volume fraction than 30 wt% of talc.
Table 3. Filler loading by application and polymer, with the source of every figure.
| Application and polymer | Filler | Loading | Why | Source |
|---|---|---|---|---|
| uPVC drainpipe (additives for pipes) | Calcium carbonate | 15-20 wt% | Cost and stiffness | Reference data, secondary |
| uPVC window profile | Stearate-coated chalk or marble | 5-15 wt% | Cost, impact, surface | Reference data, secondary |
| uPVC pressure pipe | Calcium carbonate | 0.0-5.0 phr (5.00 phr = 4.63 wt% of a 108.03 phr recipe) | Process aid and cost, capped by pressure rating | PPI TR-2 (2023) |
| Vinyl siding substrate | Ground limestone | About 15 % | Cost and stiffness in the unseen layer | Reference data, secondary |
| PVC cable insulation (additives for wire and cable compounds) | Chalk 10 phr, with ATH 45-100 phr | 10 phr chalk | Cost, with ATH carrying the fire performance | Huber reference formulation |
| Polypropylene compounds | Calcium carbonate | 20-40 wt% | Cost, impact when fine and coated | Reference data, secondary |
| Automotive polypropylene (additives for automotive plastics) | Talc | 10-40 wt% | Stiffness and heat deflection | Our talc sources |
| Polypropylene and polystyrene | Barium sulfate | Up to 70 % | Density, damping, radiopacity | Reference data, secondary |
| PE film antiblock (additives for packaging film) | Diatomaceous earth or talc | 2,500-10,000 ppm | Stops film layers welding | Ampacet antiblock data |
| PE film antiblock | Calcium carbonate | 2,500-20,000 ppm | Same job, lower efficiency per particle | Ampacet antiblock data |
| PE breathable film | Fine ground calcium carbonate | See the page | Pore nucleation during biaxial stretching | Our calcium carbonate sources |
| Nylon 6 nanocomposite | Montmorillonite | 4.7 wt% | Heat deflection to 152 °C | Kojima et al., J. Mater. Res. 8 (1993) 1185 |
| Polyolefin food packaging | Organoclay | At most 12 % w/w | Regulatory ceiling, dry foods | EU 10/2011 FCM 1030 |
| PLA water bottles | Organoclay | At most 4.0 % w/w | Regulatory ceiling, long-term water storage | EU 10/2011 FCM 1075 |
| Medical tubing and catheters (additives for medical plastics; radiopaque fillers for medical plastics) | Barium sulfate | See the page | X-ray visibility | Our barium sulfate sources |
| WPC decking (additives for wood-plastic composites) | Wood flour | About 60 % of an rHDPE profile | Bulk and wood character | Published rHDPE WPC formulation |
| Conductive polypropylene | MWCNT | 0.06-1.4 wt% reported | Electrical percolation | Reported percolation studies |
Most processors never weigh a mineral powder, because the filler arrives pre-dispersed. A filler masterbatch is a concentrate of filler in a carrier resin, let down at the machine; carrier, calcium carbonate content and let-down ratio are covered on filler masterbatch. Where the mineral is fed as a powder it is side-fed into the melt rather than added at the main throat, so the screw does dispersive rather than melting work; side feeding of minerals and fibres is covered on plastic compounding.
Which Filler for Which Polymer?#
Each polymer takes the filler that fits its weakness and its processing window: PVC takes calcium carbonate because it is cheap and neutralises hydrogen chloride, polypropylene takes talc because it stiffens and nucleates at once, and polyamide takes wollastonite or calcined kaolin when the part must not warp. The matrix below pairs the 8 polymer groups with the minerals normally used in them.
Table 4. Polymer and filler matrix.
| Polymer | Fillers normally used | Why this pairing | Formulation guide |
|---|---|---|---|
| PVC | Calcium carbonate (GCC and PCC), calcined kaolin | Cost, HCl scavenging, volume resistivity in cable | additives for PVC |
| Polypropylene | Talc, calcium carbonate, wollastonite, glass fibre | Stiffness and nucleation, cost, strength without warpage | additives for polypropylene |
| Polyethylene | Calcium carbonate, diatomaceous earth, talc, silica, nepheline syenite | Cost in film, antiblock, breathable film pores | additives for polyethylene |
| Polyamide | Wollastonite, calcined kaolin, mica, glass fibre | Low warpage and heat deflection | additives for nylon |
| PC and ABS | Talc, mica, glass fibre | Flat, stiff housings with controlled shrinkage | See the polymer guides |
| POM and PTFE | Aramid and glass | Wear and bearing performance | See the polymer guides |
| PPS and PEEK | Glass fibre and carbon fibre | Stiffness and strength at high service temperature | See the polymer guides |
| PLA | Calcium carbonate, talc for nucleation, natural fibres, organoclay | Crystallisation rate, cost, barrier | additives for PLA; fillers for PLA and biopolymers |
Fillers for polypropylene#
Polypropylene is the polymer that takes the widest range of fillers, and the choice is essentially between talc for stiffness and heat, calcium carbonate for cost and impact, and glass fibre when the part has to carry load. Talc runs at 10 to 40 wt% as a filler, sold as T10 to T40 grades named after the loading, and at 0.5 to 5 wt% it acts instead as a nucleating agent. Calcium carbonate runs at 20 to 40 %, and the fine, stearic-acid-coated grades below about 3 µm are the ones that can raise notched impact rather than lower it.
Two interactions decide whether a filled polypropylene survives its service life. Talc adsorbs part of the phenolic antioxidant and hindered amine package, so a talc-filled compound needs a stronger stabilizer dose. Glass-fibre polypropylene needs a maleic-anhydride-grafted polypropylene in the matrix to couple with the amino-silane sizing on the fibre; published work puts the optimum at 1 wt% for flexural strength, a gain of 24.7 %, and at 3 wt% for tensile strength, modulus and impact. One further trap is not a filler at all: phthalocyanine pigments nucleate polypropylene and can cause warpage. The talc-versus-calcium-carbonate trade-off is worked through on fillers for polypropylene.
Fillers for PVC#
PVC is the largest single consumer of calcium carbonate among plastics, and the loading changes completely between a pressure pipe, a window profile and a cable compound. The spread is wide: a uPVC drainpipe carries 15 to 20 %, a window profile 5 to 15 % of coated chalk or marble, vinyl siding substrate about 15 % of ground limestone, and a flexible cable compound up to 70 phr. Rigid pressure pipe is the exception, because the PPI TR-2 reference recipe allows only 0.0 to 5.0 phr, and in the worked 108.03 phr example 5.00 phr is 4.63 wt% of the compound; the pressure rating, not the cost, sets that ceiling.
Calcium carbonate earns its place for a chemical reason as well as a commercial one, because it neutralises the hydrogen chloride released as the polymer degrades, which supports rather than competes with the heat stabilizer, and precipitated and nano-precipitated grades act as impact co-modifiers in rigid PVC. Two other minerals have defined jobs: calcined kaolin raises the volume resistivity of wire insulation, and in flexible compounds the oil absorption of the filler competes for plasticizer, so a high-absorption mineral hardens the compound at constant plasticizer dose. Pipe, profile and cable loadings are set out on fillers for PVC.
Fillers for polyethylene film#
Polyethylene film uses filler in two very different ways: as a cost-cutting calcium carbonate masterbatch in bags and sacks, and as a functional particle that makes a stretched film breathable or stops its layers blocking. The cost route is straightforward, since the filler arrives as a concentrate in a polyethylene carrier and is let down at the blown-film line. The functional routes are more demanding. Fine ground calcium carbonate nucleates the pores of breathable microporous film during biaxial stretching, so the particle size distribution, not the loading, sets the water-vapour transmission rate. Antiblock particles work at ppm level: diatomaceous earth and talc at 2,500 to 10,000 ppm, calcium carbonate at 2,500 to 20,000 ppm.
Density is the hidden constraint. Guidance from the Association of Plastic Recyclers asks that film be tested as its density approaches 0.996 g/cm3, and above 1.00 g/cm3 it is not recyclable in a float-sink stream, which limits how much mineral a film can carry whatever the cost case says. Masterbatch and breathable film are covered on fillers for polyethylene.
Fillers for polyamide and other engineering plastics#
Engineering polymers are filled for dimensional stability rather than for cost, which is why polyamide, PBT and PC/ABS take wollastonite, calcined kaolin and mica alongside or instead of glass fibre. Mineral-reinforced polyamide exists because a part carrying unidirectional short glass shrinks differently along and across the flow, and the three low-warpage minerals do not. The nanocomposite route reaches the same target without the abrasion of a mineral loading ten times larger. Moisture is the competing variable, since water uptake lowers the modulus of polyamide and no filler prevents that. Low-warpage mineral packages are compared on mineral fillers for nylon.
Glass remains the reference reinforcement here, and its numbers are regulatory as much as mechanical. Flame-retardant polyamides carry 10 to 50 % glass fibre in the Clariant Exolit OP data, the sizing silane FCM 1068, CAS 2530-83-8, is authorised under Regulation (EU) No 10/2011 only in sizing for glass fibre embedded in PET, PC, PBT, thermoset polyesters and epoxy bisphenol vinylester, and 21 CFR 177.2410 lists diatomaceous earth, glass fiber and mica as phenolic adjuvants. GF30 and GF50 grades are covered on glass-filled nylon.
Why Fillers Are Surface Treated: Stearic Acid, Silanes and Coupling Agents#
A mineral surface is polar and a polyolefin is not, so an untreated filler disperses badly, raises viscosity and weakens the compound, and 3 different treatments exist to fix that. Surface chemistry, not loading, usually separates a filled compound that works from one that does not, and the stearate, silane and titanate routes are compared on filler surface treatment. The 3 routes are listed below.
- Non-reactive coating on the filler. Stearic acid on calcium carbonate is the archetype: the fatty acid lies down on the carbonate surface, makes it organophilic and lets the particle disperse. That coating makes calcium carbonate toughening possible, because the MIT and Twente results depend on stearic-acid-coated grades below about 3 µm that debond cleanly instead of agglomerating.
- Reactive coupling on the filler. Silanes are applied to glass, silica, wollastonite and kaolin and form a covalent bridge between mineral and polymer; titanates and zirconates do a comparable job on carbonates. Maleated polyolefins and titanates are covered on coupling agents for filled and reinforced plastics.
- Coupling from the matrix side. Instead of treating the particle, the formulator adds a functionalised polymer to the matrix. Maleic-anhydride-grafted polypropylene couples an amino-silane-sized glass fibre to polypropylene at an optimum of 1 wt% for flexural strength and 3 wt% for tensile, modulus and impact, and the same chemistry makes wood flour usable.
Treatment demand scales with surface area rather than weight, so a fumed silica at 50 to 600 m2/g needs far more treatment per kilogram than a coarse ground carbonate, while glass fibre sizing sits at 0.5 to 2.0 wt% of the fibre. Treatment is not always worth paying for: in a high-loading extender application where strength is not the specification, an uncoated mineral can be the correct answer. The silane chemistries and their dosing are covered on silane coupling agents.
How Do You Select a Filler for a Plastic? 7 Steps#
Select a filler for a plastic in 7 steps: name the property gap, fix the polymer and the processing temperature, choose the particle shape, set the loading by volume, choose the surface treatment, screen the regulations, then check the side effects and test. The sequence matters, because a decision taken at step 3 constrains everything after it.
- Name the property you need and the property you are willing to sacrifice. Stiffness is usually bought with impact strength, and density with part weight.
- Fix the polymer, the processing method and the melt temperature before looking at minerals.
- Choose the shape: blocky for isotropy and flow, platy for stiffness and barrier, acicular or fibrous for strength, hollow for weight reduction.
- Set the loading in vol% first, then convert to wt% and phr for costing, because volume fraction governs modulus and percolation while weight fraction governs cost and density.
- Check the surface treatment and decide whether the coupling is paid for on the particle or in the matrix.
- Screen the regulatory status for every target market: the food-contact entry, the dust classification and, for any particle below 100 nm, the nanoform rules.
- Confirm by testing after checking the side effects: melt viscosity, machine wear, stabilizer adsorption, compound density and recyclability.
Two side effects should be priced in before the trial. Abrasion follows Mohs hardness, so a switch from talc at 1 to wollastonite at 4.5 to 5 changes the screw and barrel specification, and a loading that pushes a polyolefin above 1.00 g/cm3 removes it from float-sink sorting. The framework for every additive family is on how to select plastic additives.
How Are Filler Content and Filler Performance Tested?#
Filler content itself is measured by burning the polymer away: ash content to ISO 3451-1 or ASTM D5630, or thermogravimetric analysis when the filler also decomposes. One caveat applies to the commonest filler of all. Carbonate fillers decompose during ashing and thermogravimetric analysis, so the residue left by a calcium-carbonate-filled compound is calcium oxide, not calcium carbonate, and the raw residue figure understates the original filler content unless the method accounts for the loss. Performance is then measured on the compound rather than on the powder, with stiffness, heat resistance, impact, thermal transport and electrical insulation each carrying its own standard. Every method below is indexed under testing plastic additives.
Table 5. Filler properties and the standards that measure them.
| Property | Method | Standard |
|---|---|---|
| Filler content (ash content and filler content testing) | Ashing, or TGA for decomposing fillers | ISO 3451-1, ASTM D5630 |
| Glass content of reinforced plastics (fibre length and glass content measurement) | Calcination | ISO 1172 |
| Density of the compound | Immersion | ISO 1183, ASTM D792 |
| Particle size distribution | Laser diffraction | ISO 13320 |
| Specific surface area | BET nitrogen adsorption | ISO 9277 |
| Oil absorption | Spatula rub-out | ISO 787-5, ASTM D281 |
| Heat deflection temperature | Three-point loading under flexural stress | ISO 75, ASTM D648 |
| Flexural modulus and strength | Three-point bending | ISO 178 |
| Impact strength | Charpy and Izod | ISO 179, ISO 180 |
| Thermal diffusivity and conductivity | Transient plane source, laser flash, thermal interface method | ISO 22007-2, ASTM E1461, ASTM D5470 |
| Volume resistivity | DC resistance measurement | IEC 62631-3-1 |
How Are Fillers for Plastics Regulated?#
Fillers are regulated in 4 layers: chemical registration, where most natural minerals are exempt; food contact, where each filler needs a named entry; hazard classification, which currently concerns crystalline silica, talc and carbon nanotubes; and workplace dust limits. The first layer surprises newcomers. Points 7 and 8 of Annex V to Regulation (EC) No 1907/2006 exempt naturally occurring minerals that are not chemically modified, and point 11 covers glass and ceramic frits, which is why kaolin, wollastonite, mica, dolomite, montmorillonite, bentonite, nepheline syenite, limestone, halloysite and cristobalite carry no REACH dossier under those identities, while manufactured fillers such as precipitated calcium carbonate, synthetic amorphous silica, alumina, graphite, graphene, flux-calcined diatomite, calcined kaolin and talc are registered. Since Regulation (EU) 2018/1881 registrants must also describe the nanoforms they place on the market. All four layers are summarised in plastic additive regulations.
Table 6. Regulatory status of the fillers used in plastics. REACH status is the registration position of the identity named in the CAS column, checked in ECHA CHEM on 22 September 2026; an organically modified or calcined grade can have a different identity and a different obligation.
| Filler | CAS | EC | REACH status | EU 10/2011 FCM No and restriction | US FDA route | Other |
|---|---|---|---|---|---|---|
| Ground calcium carbonate (GCC) | 471-34-1 | 207-439-9 | Annex V exempt, unmodified natural mineral | FCM 21, carbonic acid salts, no SML | 21 CFR 184.1191 (GRAS), 178.3297 | Ground limestone also carries CAS 1317-65-3 |
| Precipitated calcium carbonate (PCC) | 471-34-1 | 207-439-9 | Registered, 296 active dossiers | FCM 21 | 21 CFR 184.1191, 178.3297 | See precipitated calcium carbonate (PCC) |
| Dolomite | 16389-88-1 | 240-440-2 | No dossier, Annex V | FCM 623, no SML | Not named | Density 2.85 g/cm3, Mohs 3.5-4 |
| Talc | 14807-96-6 | 238-877-9 | Registered, 15 active dossiers | FCM 615, no SML | 21 CFR 178.3297, 182.90 | RAC opinion of 20 Sep 2024 proposes Carc. 1B H350 and STOT RE 1 H372; IARC 2A (2024). See talc |
| Kaolin | 1332-58-7 | 310-194-1 | No dossier, Annex V | FCM 410; particles thinner than 100 nm only below 12 % w/w in an EVOH inner layer behind a functional barrier; Annex II Al SML 1 mg/kg | 21 CFR 186.1256 (GRAS, paper), 178.3297 as aluminum silicate (China clay) | Calcination above about 400 °C is irreversible |
| Calcined kaolin | 92704-41-1 | 296-473-8 | Registered, 4 active dossiers | FCM 753; Annex II Al SML 1 mg/kg | Not named separately in 178.3297 | See calcined kaolin |
| Mica | 12001-26-2 | 601-648-2 | No dossier, Annex V | FCM 597, no SML | 21 CFR 178.3297, 177.2600, 177.2410 | Aspect ratio 20-100 |
| Wollastonite | 13983-17-0 | 237-772-5 | No dossier, Annex V | FCM 613, no SML | Not named | IARC Group 3 (vol. 68, 1997) |
| Barium sulfate | 7727-43-7 | 231-784-4 | Registered, 49 active dossiers | No named entry; permitted under Art. 6(3)(a) as a salt of sulphuric acid, FCM 511; Annex II Ba SML 1 mg/kg | 21 CFR 178.3297, 177.2600 | Water solubility 0.00031 g/100 g at 20 °C |
| Synthetic amorphous silica | 7631-86-9 | 231-545-4 | Registered, 371 active dossiers | FCM 504, with the nanoform specification 1-100 nm primaries aggregated to 0.1-1 µm | 21 CFR 172.480, 178.3297, 177.2600, 182.90 | 112945-52-5 and 112926-00-8 are former CAS numbers only |
| Silanated silica | 7631-86-9 | 231-545-4 | Covered by the SAS registration | FCM 87 | As for SAS | Surface-modified grade |
| Fumed silica | 7631-86-9 | 231-545-4 | Covered by the SAS registration | FCM 504 | As for SAS | See fumed silica |
| Precipitated silica | 7631-86-9 | 231-545-4 | Covered by the SAS registration | FCM 504 | As for SAS | See precipitated silica |
| Cristobalite | See the page | See the page | See the page | FCM 614 | Not named | Respirable crystalline silica limits apply |
| Quartz | See the page | See the page | See the page | FCM 616 | Not named | Respirable crystalline silica limits apply |
| Diatomaceous earth, natural | 61790-53-2 | EC list 612-383-7 | No dossier, Annex V | FCM 707, no SML | 21 CFR 178.3297, 182.90, 177.2410 | 80-90 % silica |
| Diatomaceous earth, flux-calcined | 68855-54-9 | 272-489-0 | Registered, 19 active dossiers | FCM 734, no SML | 21 CFR 178.3297, 182.90 | Contains crystalline silica |
| Glass fibre | Not applicable | Not applicable | Amorphous glass fibre, 11 active dossiers | FCM 38; sizing silane FCM 1068 (CAS 2530-83-8) only in sizing for glass fibre in PET, PC, PBT, thermoset polyesters and epoxy bisphenol vinylester | 21 CFR 177.2410 | IARC Group 3 for continuous filament glass (vol. 81, 2002) |
| Glass microballs | Not applicable | Not applicable | Annex V point 11, glass | FCM 39, no SML | Not named | Up to 80 % breakage possible in standard equipment |
| Montmorillonite and bentonite | 1318-93-0 (MMT); 1302-78-9 (bentonite) | 215-288-5 | No dossier under the natural identity, Annex V | Bentonite FCM 393 | 21 CFR 178.3297 (bentonite; dimethyldioctadecylammonium bentonite) | See montmorillonite (organoclay) |
| Organoclay, FCM 1030 | See the page | See the page | See the page | At most 12 % w/w in polyolefins for dry foods at room temperature or below; sum of 1-chlorohexadecane and 1-chlorooctadecane at most 0.05 mg/kg | Not named | Platelets parallel to the surface and fully embedded |
| Organoclay, FCM 1075 | See the page | See the page | See the page | At most 4.0 % w/w in PLA for long-term water storage | Not named | Platelets parallel to the surface and fully embedded |
| Halloysite | 12068-50-7 | 686-506-8 | No dossier, Annex V | Not listed | Not named | Tube, aspect ratio 5-20, BET up to 117 m2/g |
| Boron nitride (hexagonal) | 10043-11-5 | 233-136-6 | See the page | FCM 583, group restriction 16, SML(T) 6 mg/kg as boron | Not named | See boron nitride |
| Aluminium nitride | 24304-00-5 | 246-140-8 | Registered, 6 active dossiers | Not listed in Annex I | Not named | 70-210 W/(m·K) polycrystalline |
| Aluminium oxide (alumina) | 1344-28-1 | 215-691-6 | Registered, 458 active dossiers | FCM 418; Annex II Al SML 1 mg/kg | Not named | Distinct from ATH, Al(OH)3, CAS 21645-51-2. See aluminum oxide (alumina) |
| Graphite | 7782-42-5 | 231-955-3 | Registered, 146 active dossiers | FCM 521, no SML | Not named | See graphite |
| Carbon nanotubes (MWCNT) | 308068-56-6 | 608-533-6 | See the page | No Annex I entry; nanoforms only if explicitly authorised, Art. 9(2) | Not named | CLP index 006-104-00-2: Carc. 1B H350i, STOT RE 1 H372, in application from 1 May 2026 |
| Graphene | 1034343-98-0 | 801-282-5 | Registered, 9 active dossiers | No Annex I entry | Not named | See graphene in plastics |
| Cellulose and lignocellulose | See the page | See the page | See the page | Cellulose FCM 553 as additive and monomer; lignocellulose FCM 595 only as monomer or starting substance | Not established | The two entries are not interchangeable |
Every substance record behind this table, with its full identifier set and dosage data, sits in the plastic additives database.
Food contact: EU 10/2011 entries and the US FDA routes#
A filler may be used in an EU food-contact plastic only if it has an entry on the Union list of Regulation (EU) No 10/2011, and 26 filler entries exist, from carbonic acid salts (FCM 21) to the two organoclays (FCM 1030 and 1075). The full set runs FCM 21 carbonic acid salts, 38 glass fibers, 39 glass microballs, 84 and 85 natural and silanated natural silicates, 86 silylated silicic acid, 87 silanated silicon dioxide, 393 bentonite, 410 kaolin, 417 silicic acid, 418 aluminium oxide, 504 silicon dioxide, 521 graphite, 553 cellulose, 583 boron nitride, 597 mica, 613 wollastonite, 614 cristobalite, 615 talc, 616 quartz, 623 dolomite, 684 nepheline syenite, 707 and 734 natural and flux-calcined diatomaceous earth, 753 calcined kaolin and 1068 the glass-fibre sizing silane. The Union list and its restrictions are explained on EU 10/2011. Two constraints apply whether or not the entry carries its own limit: the Annex II metal specific migration limits of 1 mg/kg for aluminium and barium, 5 mg/kg for zinc, 48 mg/kg for iron and 0.6 mg/kg for manganese and lithium, with no limit for calcium, magnesium, potassium and sodium; and Article 9(2) on nanoforms.
The United States works differently, and the difference is routinely misread: no filler is "FDA approved" for plastics as such. 21 CFR 178.3297 lists mica, China clay, barium sulfate, bentonite, calcium carbonate, calcium silicate, diatomaceous earth, talc and silica as colorants for polymers, permitted only at the level needed for the colouring effect, so that section does not authorise filler-level loadings. Filler-level use rests instead on GRAS or prior-sanctioned status plus the regulation covering the polymer: 184.1191, 186.1256, 182.90, 172.480, 177.2600 and 177.2410. Those routes are mapped on FDA food contact rules.
Dust, classification and worker exposure: silica, talc and carbon nanotubes#
The health question about mineral fillers is a dust question, not a migration question: the hazard sits with the airborne respirable fraction handled in the compounding plant, not with the particle locked inside a finished part. Respirable crystalline silica is the clearest case. Directive (EU) 2017/2398, amending Directive 2004/37/EC, sets a binding occupational limit value of 0.1 mg/m3 for the respirable fraction, and 29 CFR 1910.1053 sets an OSHA permissible exposure limit of 50 µg/m3 as an 8-hour time-weighted average with an action level of 25 µg/m3. The NEPSI social-dialogue agreement of 2006 covers good handling practice, and calcined diatomaceous earth falls inside those limits even though the natural grade does not. The Annex V exemption is explained on REACH and plastic additives.
Three classification files are open or newly closed. For talc, the Risk Assessment Committee opinion adopted on 20 September 2024 recommends Carc. 1B H350 and STOT RE 1 H372, a proposal and not an entry in Annex VI to Regulation (EC) No 1272/2008; the International Agency for Research on Cancer placed asbestos-free talc in Group 2A in July 2024 and talc containing asbestos in Group 1. For crystalline silica, a CLH opinion was adopted on 7 March 2025 and no harmonised classification is in force. For carbon nanotubes, the entry applies from 1 May 2026 under Commission Delegated Regulation (EU) 2024/2564. Proposition 65 wording repays care: the listings are crystalline silica of respirable size (1 October 1988) and talc containing asbestiform fibers (1 April 1990), so asbestos-free plastics-grade talc is not the listed substance. Pending and applied entries are tracked on CLP classification of plastic additives.
Who Supplies Fillers for Plastics? Minerals, Market and Prices#
Fillers are the largest additive group by tonnage: more than 19.5 million tonnes of the 36.7 million tonnes of plastic additives consumed worldwide in 2023, according to Ceresana. The same study puts plasticizers above 8 million tonnes and Asia-Pacific above 50 % of consumption, while a second reading of the same market puts plasticizers first at 34 % of additive consumption by weight and fillers second at 28 %. Rankings differ because analysts count mineral fillers and reinforcing minerals differently. Segment and region data are broken out on plastic additives market.
Table 7. Producers of fillers for plastics.
| Producer | Headquarters | Minerals and particles | Brands and notes |
|---|---|---|---|
| Omya | Oftringen, Switzerland | GCC and PCC | Founded 1884, about 9,000 employees |
| Imerys | See directory | Talc, kaolin, wollastonite, diatomite | Its North American talc business filed for Chapter 11 on 13 February 2019; the assets went to Magris Resources in November 2020 for USD 223 million |
| Minerals Technologies / Specialty Minerals | See directory | Precipitated calcium carbonate | |
| J.M. Huber (Huber Advanced Materials) | Atlanta, United States | Alumina hydrate and magnesium hydroxide products | Founded 1883; Martinal, Magnifin, Micral, Hydral |
| Elementis (Mondo Minerals) | See directory | Talc | |
| IMI Fabi | See directory | Talc | |
| Imerys NYCO | See directory | Wollastonite | |
| Vanderbilt | See directory | Wollastonite | |
| Wolkem | See directory | Wollastonite | |
| 3M | See directory | Hollow glass microspheres | |
| Potters | See directory | Glass spheres | |
| Evonik | See directory | Fumed silica | Aerosil |
| Cabot | See directory | Fumed silica, carbon nanotubes | Cab-O-Sil |
| Wacker | See directory | Fumed silica | HDK |
| Tokuyama | See directory | Fumed silica | Reolosil |
| OCI | See directory | Fumed silica | Konasil |
| Heraeus, Orisil, Xunyuchem | See directory | Fumed silica | |
| Syensqo and PPG | See directory | Precipitated silica | |
| BYK | See directory | Organoclay | Cloisite |
| OCSiAl, Nanocyl, LG Chem, Cnano | See directory | Carbon nanotubes | |
| Denka, Resonac | See directory | Boron nitride | |
| Imerys, EP Minerals | See directory | Diatomite |
Company profiles sit in the directory of plastic additive manufacturers and suppliers, and grades, locations and certifications are compared on calcium carbonate and mineral filler suppliers.
Prices are published annually by the United States Geological Survey as US unit values, which are mineral prices, not compound prices. For 2024 the USGS reports talc at USD 330 per tonne milled, ground mica at USD 300 per tonne dry-ground, ground barite at USD 220 per tonne, kaolin at USD 160 per tonne and diatomite at USD 590 per tonne. Substitution is real: the USGS names bentonite, kaolin, mica and wollastonite as substitutes for talc in plastics, and the US Environmental Protection Agency's chrysotile asbestos ban, a final rule of 28 March 2024, affects asbestos-containing talc and drives demand for wollastonite. Grade-to-grade pricing is set out on calcium carbonate filler price.
How Do Fillers Differ from Pigments, Mineral Flame Retardants and Reinforcing Fibres?#
A particle is classed by the job it is bought for, not by its chemistry, which is why talc is a filler at 20 wt% and a nucleating agent at 1 wt%, and why aluminium trihydrate is a flame retardant even though it is a mineral powder used at filler-like loadings. The same mineral can appear in two families on this site, and the loading is usually what tells them apart.
Table 8. The 4 neighbouring particle families.
| Family | What the particle is bought for | Typical members | Overlap with fillers |
|---|---|---|---|
| colorants for plastics | Colour and opacity | Titanium dioxide, carbon black, iron oxides | All are particles; none is a filler on this site, and 21 CFR 178.3297 lists several fillers as colorants at colouring-effect levels only |
| mineral flame retardants (ATH and MDH) | Endothermic water release | Aluminium trihydrate, magnesium dihydroxide | ATH releases water from about 200 °C (1,051 J/g) and MDH is stable to about 320 °C (1,316 J/g); both are dosed at filler-like levels |
| antiblock additives | Surface roughness in film | Diatomaceous earth, silica, talc, kaolin, nepheline syenite | The same minerals, dosed at ppm rather than wt% |
| nucleating agents | Faster, finer crystallisation | Talc among others | Talc at 0.5-5 wt% nucleates; at 10-40 wt% it fills |
Do fillers make plastic harder to recycle?#
Mineral filler is the quiet reason a polyolefin part fails float-sink sorting: minerals are 2.6 to 4.5 times denser than polyethylene, so a compound that started at 0.95 g/cm3 can cross 1.00 g/cm3 and sink with the PET. Guidance from the Association of Plastic Recyclers asks that polyethylene film be tested as its density approaches 0.996 g/cm3 and treats film above 1.00 g/cm3 as not recyclable, and mineral-filled polypropylene above 1.0 g/cm3 sinks in the same way. Density, not chemistry, is what the sorting plant measures, and the rules that follow are on design for recycling.
Regulation moves in the same direction. The Packaging and Packaging Waste Regulation, Regulation (EU) 2025/40, applies from 12 August 2026 and introduces recyclability performance grades, so a filler decision taken for cost carries a compliance consequence. No numeric filler ceiling is published in the sources used here, and none should be assumed. Restabilizing a filled recyclate is covered on additives for recycled plastics.
Are mineral fillers in plastics safe?#
Most mineral fillers carry no harmonised hazard classification, and the notifications that exist are for eye and airway irritation, so the safety question is about handling powder in the compounding plant rather than about the finished part. Self-classification notifications for calcium carbonate, barium sulfate, talc, alumina, dolomite and silica mostly report "not classified", with a minority citing H319 for serious eye irritation and H335 for respiratory irritation. The limits that do apply are occupational: 0.1 mg/m3 for respirable crystalline silica in the European Union and an OSHA permissible exposure limit of 50 µg/m3 in the United States.
Three files sit outside that calm picture, all concerning inhaled dust rather than migration: the proposed talc classification, the IARC Group 2A listing of asbestos-free talc from July 2024, and the carbon nanotube entry of 1 May 2026. Litigation follows the same fault line, with a USD 4.7 billion verdict in 2018, about 38,000 pending suits in 2023 and one US talc miner selling its talc subsidiary in April 2024 because of legal disputes (USGS). The additives that do raise substantive concern are listed on toxic plastic additives.
Fillers in rubber, TPE and thermoset composites#
Rubber and thermoset composites use several of the same minerals as thermoplastics, and this reference covers them only where the filler is shared. Precipitated silica is the clearest shared case, since it is the reinforcing filler of rubber and shoe soles, with production above 1 million tonnes in 1999 and about half going to tyres and soles. 21 CFR 177.2600 permits aluminum hydroxide, aluminum silicate, barium sulfate, carbon black at at most 50 % of the rubber product, cork, cotton, mica, nylon, silica, titanium dioxide, zinc carbonate and zinc sulfide in repeat-use rubber articles, and still carries legacy text naming chrysotile and crocidolite asbestos. Unsaturated polyester sheet and bulk moulding compounds use calcium carbonate, aluminium trihydrate and chopped glass longer than one inch, while epoxy potting uses silica, alumina, boron nitride and aluminium nitride. The shared minerals are listed on fillers for rubber and TPE.
A short history of fillers in plastics#
The filler story starts with wood flour in Bakelite, the first moulded composite, and its two turning points are the industrial glass fibre of the late 1930s and the Toyota nylon 6-clay hybrid of 1993, which showed that a few per cent of a nanometre-thin platelet could do the work of 30 per cent of a mineral. Games Slayter at Owens-Illinois filed a glass-wool patent in 1933, commercial glass fibre production began in 1936 and Owens-Corning Fiberglas was formed in 1938. Paul Dhe's basalt fibre patent, US 1,462,446, dates from 1923, and wood-plastic composite was invented by Covema in Milan in 1960.
Frequently asked questions about fillers for plastics#
The four questions below are the ones asked most often about fillers for plastics, answered directly.
What is the most used filler in plastics?#
Calcium carbonate is the most used filler in plastics by a wide margin, because it is the cheapest mineral that disperses well, and it goes into PVC, polypropylene and polyethylene at 5 to 70 phr. Fillers as a group exceed 19.5 million tonnes of the 36.7 million tonnes of plastic additives consumed worldwide in 2023 (Ceresana). Talc is second in engineering and automotive polypropylene, and plastics take 32 % of US talc sales (USGS, 2024).
Does calcium carbonate weaken plastic?#
It depends on the grade: coarse uncoated calcium carbonate lowers tensile strength because the particles debond and act as voids, while fine stearic-acid-coated grades below about 3 µm can raise the notched impact strength of polypropylene. The MIT work of Thio and co-workers in 2002 and the Twente work of Zuiderduin and co-workers in 2003 describe that toughening route. The failure mode is dispersion, since agglomerates and coarse top-cut particles initiate cracks.
What does "30 % glass filled" mean?#
"30 % glass filled", written GF30, means that 30 % of the compound weight is glass fibre, not 30 % of its volume. Glass is roughly twice as dense as the polyamide it is compounded into, so the volume fraction is considerably lower than the weight fraction, and the volume fraction governs stiffness. GF grades and their properties are set out on glass fiber reinforced plastics.
Plastic filler in compounding, plastic body filler and dermal fillers#
Three different products share the word: a filler in plastics compounding is a mineral powder mixed into the polymer melt, a plastic body filler is a two-part polyester putty used to repair a car bumper, and a dermal filler is an injectable cosmetic gel. Only the first is a plastic additive, and it is the only one covered here.