Aluminum Trihydrate (ATH, Alumina Trihydrate): Flame Retardant Filler for Plastics

Aluminum trihydrate (ATH, aluminium hydroxide, Al(OH)3, CAS 21645-51-2) is a mineral flame retardant filler that cools a burning polymer by releasing 34.6 % of its own weight as water vapour from about 200 °C (392 °F). Because that water release is the whole mechanism, ATH is dosed at 30 to 65 wt%, not at the 1 to 20 wt% typical of chemical flame retardants, and that single fact changes every other property of the compound.

This page covers ATH as a plastics additive, not the antacid tablet, the vaccine adjuvant or the ceramics raw material that share its CAS number. Its regulatory position is settled on every EU instrument that touches it: aluminium hydroxide is registered under REACH, is absent from the Candidate List of Substances of Very High Concern, carries no harmonised classification under the CLP Regulation and is an authorised food-contact additive as FCM substance 629 under Regulation (EU) No 10/2011. ATH is one of 87 flame-retardant pages in this directory of plastic additives, each carrying the same identity, dosage and regulatory fields.

This reference sets out the identity and naming of ATH, its endothermic mechanism and smoke suppression, its physical properties, the loading it takes in each polymer, its 6 applications in plastics, its LOI, UL 94 and cone calorimeter performance, its behaviour beside other additives, its dated regulatory matrix, its health and environmental profile, the comparison against magnesium hydroxide, boehmite and huntite-hydromagnesite, and the producers and grades on the market.

Table T1. Identity of aluminum trihydrate (ATH).

What Is Aluminum Trihydrate (ATH)?#

ATH is aluminium hydroxide, Al(OH)3, a white mineral powder of hexagonal platelets that works in plastics as both a flame retardant and a functional filler. It belongs to the metal hydroxide class, has a molecular weight of 78.00 g/mol, and shares that class with magnesium hydroxide, boehmite and huntite-hydromagnesite. The dual function is the reason it is bought: the same particles that release water in a fire occupy volume, stiffen the compound and replace resin.

Which names on a data sheet all point to the same substance? Aluminium hydroxide, aluminum hydroxide, aluminum trihydrate, alumina trihydrate, aluminium trihydroxide, hydrated alumina and gibbsite all describe one compound under CAS 21645-51-2. As a mineral additive, ATH sits in the highest-loading class of flame retardants for plastics, the hub that compares every chemical family against it.

What does ATH stand for?#

ATH stands for aluminium trihydrate, the trade convention for aluminium hydroxide, which the same data sheets also call alumina trihydrate, aluminum trihydroxide or hydrated alumina. The word trihydrate describes the three hydroxyl groups that leave as water, although current chemical practice writes the formula Al(OH)3 rather than Al2O3 with three waters of hydration.

Is alumina trihydrate the same as aluminum hydroxide?#

Yes: alumina trihydrate and aluminum hydroxide are two names for one substance, CAS 21645-51-2, formula Al(OH)3. Nothing in the chemistry, the particle morphology or the fire performance changes with the name printed on the bag, and a specification written against either name buys the same mineral.

The substance that is genuinely different is alumina, aluminum oxide (alumina, Al2O3), CAS 1344-28-1, molecular weight 101.96 g/mol, which carries no water to release and serves as a thermally conductive, electrically insulating filler instead of a flame retardant. Three names, two substances: Table T2 separates them.

Table T2. Alumina trihydrate vs aluminum hydroxide vs alumina.

ATH or ATO? Why the two abbreviations are not interchangeable#

ATH is aluminium trihydrate, a halogen-free mineral with no harmonised hazard classification; ATO is antimony trioxide (CAS 1309-64-4), a halogen synergist classified Carc. 2 (H351) under the EU CLP Regulation. Antimony trioxide is also FCM substance 398 with a specific migration limit of 0.04 mg/kg expressed as antimony under Regulation (EU) No 10/2011, and it has been listed as a carcinogen under California Proposition 65 since 1 October 1990. The two minerals serve opposite purposes: ATO multiplies the effect of bromine or chlorine in the flame, while ATH is the additive of halogen-free systems.

Is ATH the same as gibbsite?#

Yes: gibbsite is the natural mineral form of aluminium hydroxide, and commercial ATH is the same compound supplied as a controlled powder with particle sizes from 0.25 to 80 µm. Grade selection therefore turns on particle size distribution and surface treatment rather than on mineralogy.

How Does ATH Work as a Flame Retardant?#

ATH retards flame by decomposing endothermically: above about 200 °C (392 °F) it splits into alumina and water, 2Al(OH)3 → Al2O3 + 3H2O, absorbing 1051 J/g (about 280 cal/g) of heat from the polymer. That heat leaves the burning surface, so the polymer stays below the temperature at which it pyrolyses fast enough to feed the flame.

Where does that heat go, and what is left behind? The energy is consumed as latent heat in converting 34.6 % of the mineral mass into water vapour, and what remains on the surface is a porous alumina residue. Aluminium hydroxide therefore acts in two of the standard flame-retardant modes at once, the gas phase and the condensed phase, which is why its loading rather than its chemistry sets its effectiveness.

ATH acts through 4 mechanisms at once, listed below.

• Endothermic cooling. Decomposition absorbs 1051 J/g, drawing heat out of the condensed phase and holding the polymer surface below its pyrolysis temperature.
• Water-vapour dilution. The released steam lowers the partial pressure of fuel gases and of oxygen in the flame zone, a gas-phase effect.
• Alumina residue. The Al2O3 left behind forms an inorganic layer that shields the unburnt polymer from radiant heat.
• Soot adsorption. That same oxide residue adsorbs soot, the route by which a mineral filler suppresses smoke as well as flame.

Endothermic cooling is one of the routes described on how flame retardants work, where radical trapping, char formation and dilution are compared side by side. The Huber cable brochure, the supplier data set used throughout this page, records the 1051 J/g figure for ATH against 1316 J/g for magnesium hydroxide, so the two minerals differ in heat absorbed per gram as well as in thermal stability.

Why does ATH also suppress smoke?#

ATH suppresses smoke because the alumina residue it leaves behind adsorbs soot, which is why cable specifications name it alongside molybdates, zinc stannate and zinc borate as a smoke suppressant. The mechanism is physical rather than chemical: soot particles that would otherwise leave the flame as visible smoke are captured on the high-surface-area oxide.

Smoke density in cables is measured under EN 61034, the 3 m cube test, and the acidity of the combustion gases under EN 60754-2. This reference holds no measured smoke-density value for an ATH compound, so the test method is named here without a number attached to it. Molybdates, zinc stannate and zinc borate are compared on smoke suppressants.

What Are the Physical and Chemical Properties of ATH?#

ATH is a white free-flowing powder of hexagonal platelets with a density of 2.42 g/cm3, a Mohs hardness of 2.5 to 3.5 and a refractive index of 1.57. Its aqueous slurry sits at pH 9 to 10, and the theoretical loss on ignition is 34.6 %, the fraction that leaves as water. Table T3 lists the properties that appear on a supplier data sheet.

Table T3. Physical and chemical properties of aluminum trihydrate.

Refractive index is the property that sends ATH into decorative castings. At 1.57 the mineral is close enough to cured unsaturated polyester and acrylic resins to be used in translucent solid-surface parts, which is a property statement rather than a supplier performance claim; no light-transmission figure is published here because none is held in this reference. Refractive index and particle size are two of the filler properties that decide how a mineral behaves in a compound, alongside aspect ratio, surface area and oil absorption.

At what temperature does ATH decompose?#

ATH starts to release water at about 200 °C (392 °F), which sets the processing ceiling: a compound containing ATH should only briefly exceed 200 °C in the extruder. Cross that line for longer and the mineral decomposes during compounding instead of during the fire, producing steam voids in the melt and a compound that has already spent its flame retardant.

Sources differ on the exact onset, and the difference is worth stating openly: the Huber cable brochure gives about 200 °C, the product literature about 220 °C (428 °F) and PubChem lists a melting point of 300 °C (572 °F). The 200 °C figure governs compounding practice and is the value used throughout this page. That temperature ceiling is the whole selection rule for mineral flame retardants (ATH and MDH), because it decides which of the two minerals a given polymer can take.

Which Polymers Use ATH, and at What Loading?#

ATH is loaded at 30 to 65 wt% in EVA, polyethylene and PVC compounds, 10 to 50 times the level of a brominated or phosphorus flame retardant, because its effect is proportional to the water it carries. No chemistry amplifies the mineral, so the formulator buys fire performance by volume and rebuilds the mechanical properties afterwards with coupling agents. The 30 to 60 wt% range reported for LSZH jackets is a reported range and needs verification against the individual compound data sheet.

How do the phr values in a cable recipe convert to weight percent? The conversion is the phr of the ingredient divided by the total phr of the formulation, multiplied by 100. In the Huber halogen-free reference formulation, 160 phr of ATH sits in a recipe totalling about 260 phr, which gives 61.5 wt%. Cable recipes state ATH in PHR (parts per hundred resin), which converts to weight percent only once the full formulation total is known.

Table T4. ATH loading by polymer.

ATH in EVA and polyethylene LSZH cable compounds#

A halogen-free low-smoke cable compound carries 160 to 180 phr ATH, the largest single ingredient by weight in the recipe. At 160 phr the mineral is 61.5 wt% of the compound, which leaves the polymer as the minority phase and makes the coupling agent package a structural requirement rather than an optimisation.

The Huber reference formulation for an HFFR EVA/LLDPE compound combines EVA at 67 phr and LLDPE at 17 phr with 16 phr of coupling agents, 160 phr of ATH and 1.0 phr of antioxidants. Silane-crosslinked polyethylene takes the loading higher, to 180 phr, with vinyl-silane coated grades chosen so that the coating chemistry does not interfere with the crosslinking reaction. Compound architectures for each cable class are set out on flame retardants for wire and cable.

Table T5. Two reference cable formulations (Huber cable brochure), in phr.

The PVC formulations reach a limiting oxygen index of 26 to 27 vol % O2 and UL 94 V-0 at 3 mm.

LSZH appears on cable specifications under 9 abbreviations, listed below.

• LSF, low smoke and fume
• LS0H, low smoke zero halogen, written with a zero
• LSOH, low smoke zero halogen, written with the letter O
• LSFH, low smoke free of halogen
• ZHFR, zero halogen flame retardant
• NHFR, non-halogen flame retardant
• HFFR, halogen-free flame retardant
• OHLS, oxygen halogen low smoke
• HFT, halogen-free thermoplastic

ATH in flexible PVC#

Flexible PVC takes 45 to 100 phr ATH, which lifts a plasticised cable compound to LOI 26 to 27 vol % O2 and UL 94 V-0 at 3 mm in the Huber reference formulations. The starting point explains the dosage: PVC is already flame retardant through the chlorine in its backbone, but the plasticizer is hydrocarbon fuel, so smoke and flaming drips rather than ignition are the problems a mineral is added to solve.

Zinc borate at 3 to 6 phr cuts smoke and dripping further in the same compound, and the Huber comparison formulations pair 50 phr ATH with 5 phr antimony trioxide where the chlorine in the resin is used as the halogen source. PVC cable insulation is specified to a minimum limiting oxygen index of 26 vol % O2, the threshold these formulations are built to clear. The rest of the recipe, plasticizer, stabilizer and chalk, is covered on flexible PVC formulations, and zinc borate has its own substance record.

ATH in thermosets: unsaturated polyester, epoxy and solid surface#

Thermosets are the second home of ATH: unsaturated polyester laminates and solid-surface castings take it at high loadings because they cure well below its 200 °C (392 °F) decomposition point. A room-temperature or 80 °C (176 °F) cure never approaches the ceiling that constrains melt processing, so loading is limited by viscosity and by the mechanical properties wanted, not by thermal stability.

Glass-reinforced unsaturated polyester laminates combine ATH at high loadings with ammonium polyphosphate and zinc borate to reach hazard levels HL2 and HL3 under EN 45545-2 for rail interiors, and epoxy laminates of the FR-4 type use ATH or boehmite as fillers beside reactive TBBPA and DOPO chemistry. No numeric loading for unsaturated polyester, epoxy or solid surface is held in this reference, so those systems are described here as formulation-specific. Laminate systems are compared on additives for epoxy resins and composites.

Which polymers cannot take ATH?#

ATH cannot be used in polypropylene, nylon, PBT or polycarbonate compounds, because those polymers are processed at 240 to 320 °C (464 to 608 °F) and ATH releases its water from about 200 °C (392 °F). The same processing window excludes most ammonium polyphosphate grades, low-molecular-weight phenolics and many amines, which is why engineering plastics carry a different flame retardant toolkit from cable compounds.

Above that ceiling the compound switches to magnesium hydroxide (MDH) flame retardant, which stays intact to about 320 °C (608 °F) and tolerates a processing temperature roughly 110 °C higher than ATH. Engineering-plastic specifications that drive the choice are typically UL 94 V-0 at 0.4 to 1.6 mm, a glow-wire ignition temperature of 775 °C (1,427 °F) and a comparative tracking index of 600 V, none of which a 200 °C mineral reaches inside a 280 °C melt.

What Is ATH Used For? 6 Applications in Plastics#

ATH is used in 6 plastics applications: halogen-free low-smoke cable, PVC cable and flooring, unsaturated polyester and epoxy composites, solid surface, building and construction plastics, and rubber and carpet backing. The 6 areas are listed below.

• Halogen-free low-smoke (LSZH/HFFR) cable insulation and sheathing, at 160 to 180 phr.
• PVC cable and flooring, at 45 to 100 phr alongside zinc borate.
• Unsaturated polyester and epoxy composites, at formulation-specific high loadings.
• Solid surface, where the mineral is both the fire retardant and the visible bulk.
• Building and construction plastics, wherever a halogen-free fire classification applies.
• Rubber and carpet backing, as a filler with fire performance attached.

Halogen-free low-smoke (LSZH/HFFR) cable#

Halogen-free cable is the largest use of ATH, because the EU Construction Products Regulation grades cables on smoke and acidity as well as flame spread, and only a mineral-filled compound reaches acidity class a1. Acidity class a1 requires a conductivity below 2.5 µS/mm and a pH above 4.3 under EN 60754-2, a combination that a chlorinated or brominated compound cannot meet because it releases acid gas by design.

The class limits set the compound. Under EN 50399, class B2ca requires flame spread of 1.5 m or less, total heat release over 1,200 s of 15 MJ or less, peak heat release rate of 30 kW or less and a FIGRA of 150 W/s or less, while class Cca allows 2.0 m, 30 MJ, 60 kW and 300 W/s. The new Construction Products Regulation, Regulation (EU) 2024/3110, applies from 8 January 2026 and keeps cables as product family 31. In the supplier cone-calorimeter comparison, ATH or MDH can delay ignition by 120 to 160 s against an unfilled reference. The full cable package, stabilizer, coupling agent and antioxidant, is on additives for wire and cable compounds.

Building and construction plastics#

Construction plastics use ATH where a halogen-free fire classification is required: wall and ceiling panels, profiles and glass-reinforced polyester laminates. The Construction Products Regulation reaches these products as well as cables, so the same halogen-free logic that governs a jacket compound governs a panel.

No EN 13501-1 euroclass for a specific ATH compound is held in this reference, and none is stated here; the class always belongs to the finished product as tested. Fire classes for building plastics are set out on additives for building and construction.

Solid surface and composite castings#

Solid surface is the one application where ATH is dosed for appearance as well as fire performance: it makes up the mineral bulk of a cast acrylic or polyester worktop. The refractive index of 1.57 is what allows the filled casting to stay translucent rather than turning chalky, and the particle size, drawn from a range of 0.25 to 80 µm, sets both the surface finish and the slurry viscosity.

No filler percentage for solid surface is recorded in this reference, so none is given. Two of the trade names sold into casting applications, MoldX and Onyx Elite, are recorded without an attributed owner and are listed here on that basis.

Rubber and carpet backing#

ATH also fills rubber compounds and latex carpet backing, and US food-contact rules list aluminum hydroxide among the fillers permitted in rubber articles intended for repeated use under 21 CFR 177.2600. That listing covers rubber, not plastics, and is not a food-contact clearance for a plastic article.

How Does ATH Perform? LOI, UL 94 and Cone Calorimeter Data#

At 45 to 100 phr in a plasticised PVC cable compound, ATH raises the limiting oxygen index to 26 to 27 vol % O2 and delivers UL 94 V-0 at 3 mm. Both numbers belong to that compound at that thickness, which is the only form in which a fire rating is meaningful.

How much ATH does a UL 94 V-0 rating take? The patent literature puts the range at 60 to 65 wt% for UL 94 V-1 to V-0 in thermoplastics generally, and a rating always belongs to a compound at a stated thickness, never to the additive on its own. Under UL 94, a V-0 result requires each afterflame to last 10 s or less, the total afterflame for 5 specimens to stay at 50 s or less, afterflame plus afterglow after the second flame application to stay at 30 s or less, and no ignition of the cotton indicator. The limiting oxygen index (LOI) method, ASTM D2863-23e1 and ISO 4589-2, measures the oxygen concentration that just sustains flaming, against about 21 vol % O2 in air.

Cone calorimeter data completes the picture, because LOI and UL 94 say nothing about how much heat a burning cable releases. Under ISO 5660-1 and ASTM E1354-26, with 35 and 50 kW/m2 the most used heat fluxes and the Huggett constant of about 13.1 MJ per kg of oxygen behind the calculation, an unfilled EVA/LLDPE reference peaks above 550 kW/m2 at 35 kW/m2. In one 2025 study published in Polymers, a phosphate low-melting glass at 10 wt% in a PE-EVA/ATH cable sheath cut the peak heat release rate to 142 kW/m2, a reduction of 52 %. The V-0 criteria and the thickness rule are explained on UL 94 flammability ratings, and ignition time and peak heat release rate come from cone calorimeter testing at 35 or 50 kW/m2.

Table T6. ATH performance indicators and their test methods.

How Does ATH Interact with Other Flame Retardants and Additives?#

ATH is rarely the only flame retardant in a compound: formulators pair it with zinc borate at 3 to 6 phr for smoke and drip control, with antimony trioxide in chlorinated systems, and with maleated coupling agents that restore the mechanical properties a 60 wt% filler destroys. ATH is combined with 3 groups of additives, listed below.

• Synergists. Zinc borate, which releases its own water above 290 °C (554 °F), and antimony trioxide at 5 phr in chlorinated systems.
• Coupling agents and compatibilizers. Maleated polyolefins such as Fusabond 226D and reactive terpolymers such as Lotader 3210, at 16 phr combined in the Huber HFFR reference.
• Stabilizers. Phenolic and phosphite antioxidants, 1.0 phr in the same reference formulation, split as Ethanox 310 at 0.75 phr and Ethaphos 368 at 0.25 phr.

Those 16 phr of coupling agent are not an accessory. Vinyl and amino grades of silane coupling agents are what make a 60 wt% mineral loading processable at all, by bonding the polymer to a particle surface that is otherwise hydrophilic and inert. The additive package also has to survive the fire test as a whole: the 2025 Polymers study cited above reached its 52 % reduction in peak heat release rate by adding a phosphate low-melting glass to an ATH-filled sheath rather than by increasing the mineral.

Particle size and surface treatment: why coated ATH grades exist#

Coated ATH grades exist because a 60 wt% mineral loading destroys elongation at break unless the particle surface is compatibilised with the polymer. Surface treatments restore that elongation, and the treatment is chosen by the reaction the compound has to survive: vinyl silane for silane crosslinking, amino silane for thermoplastics, fatty acid for dispersion.

Particle size is the second axis, running from 0.25 to 80 µm across the Huber range, with fine precipitated grades going into cable and coarse ground grades into castings. No numeric elongation-retention value is published here, because this reference records the effect and not a figure. Coating chemistries are compared on filler surface treatment.

What Is the Regulatory Status of ATH?#

ATH is registered under REACH, is not a Substance of Very High Concern, carries no harmonised CLP classification and is an authorised additive for EU food-contact plastics as FCM substance 629 (status 23 September 2026). Table T7 sets out each instrument, the status and its date.

Table T7. Regulatory status of ATH, as of 23 September 2026.

Registration, evaluation and the Candidate List process are explained on REACH and plastic additives. Three cells above are open rather than empty: the US federal status of ATH in plastics, under both the FDA food-contact rules and TSCA, and the California listing status are not established in this reference and are marked as being verified rather than asserted either way.

Is ATH REACH registered, and is it an SVHC?#

Yes, ATH is registered under REACH, Regulation (EC) No 1907/2006, and no, it is not a Substance of Very High Concern: aluminium hydroxide is absent from the Candidate List as of 23 September 2026. It is equally absent from Annex XIV, the authorisation list, and from Annex XVII, the restriction list.

The contrast with the halogenated families is the reason buyers ask. DecaBDE entered the Candidate List on 19 December 2012, HBCD on 28 October 2008, Dechlorane Plus on 15 January 2018, TBBPA on 17 January 2023 and DBDPE on 5 November 2025. Aluminium hydroxide has never appeared on the SVHC Candidate List; those five brominated and chlorinated flame retardants have.

Is ATH allowed in food-contact plastics?#

Yes, in the EU: aluminium hydroxide is listed in Annex I of Regulation (EU) No 10/2011 as FCM substance 629, reference 34560, with no substance-specific migration limit, so the overall migration limit governs it. That overall limit is 10 mg/dm2, or 60 mg/kg for articles intended for infants and young children.

The real constraint is the metal rather than the additive. Annex II of the same regulation sets a specific migration limit of 1 mg/kg for aluminium in the finished article, introduced by Regulation (EU) 2020/1245, and that limit applies whatever the source of the aluminium, whether ATH, an aluminium pigment or a catalyst residue. The Annex II metal limits and the overall migration limit are explained on EU 10/2011.

The US position is different and is not established here. Aluminum hydroxide appears in 21 CFR 177.2600 among the fillers permitted in rubber articles intended for repeated use, which is a rubber clearance and not a clearance for plastics, and no plastics-side section or food contact notification number for ATH is held in this reference. The phrase FDA approved is therefore not used on this page.

Is ATH listed under California Proposition 65?#

The Proposition 65 status of ATH is not established in this reference: no OEHHA listing entry for CAS 21645-51-2 is recorded, and absence from an internal record is not the same as verified absence from the list. Antimony trioxide, the synergist used alongside ATH in chlorinated systems, has by contrast been listed as a carcinogen since 1 October 1990. Listing dates for every flame retardant are on California Proposition 65.

Is ATH Safe? Health, Safety and Environmental Profile#

ATH carries no harmonised hazard classification under the EU CLP Regulation, and most companies that notified aluminium hydroxide to ECHA report no classification, with a minority notifying skin, eye and respiratory irritation (H315, H319, H335). The aggregated notification data on PubChem is the source of that split, and no notifier count is stated here because none is recorded.

The practical hazard is dust rather than toxicity. ATH is supplied as a powder with particle sizes from 0.25 µm upward, so handling controls, extraction and respiratory protection during compounding are the operative safety measures, not exposure limits for the substance itself. No LD50, no NOAEL and no occupational exposure limit is published on this page, because none is held in this reference. The 3 elements of the profile are listed below.

• Classification. No harmonised CLP entry; minority GHS notifications of H315, H319 and H335.
• Exposure route. Inhalable dust during handling and compounding, driven by the 0.25 to 80 µm particle range.
• Assessment. The EU FP7 ENFIRO project, grant 226563, concluded in 2012, found good environmental and health profiles for 8 halogen-free options including ATH, magnesium hydroxide, ammonium polyphosphate, aluminium diethylphosphinate, melamine polyphosphate, DOPO, zinc stannate and zinc hydroxystannate.

The health debate summarised on flame retardants and human health concerns brominated and organophosphate chemistries, whose exposure questions arise from migration out of the polymer. ATH is a non-migrating mineral with no harmonised classification, so those findings do not transfer to it, and neither does the reverse claim: a good regulatory record is not a statement that any dust is harmless.

What Are the Alternatives to ATH?#

The 3 mineral alternatives to ATH are magnesium hydroxide, boehmite and huntite-hydromagnesite, and the decomposition temperature decides between them. Each carries water or carbon dioxide into the fire and releases it endothermically; what separates them is the temperature at which the release begins and how much heat each gram absorbs.

Table T8. Mineral flame retardant comparison.

Empty cells are gaps in this reference, not zeros. Boehmite onset, mass loss and density figures circulating in supplier literature are unverified here and are deliberately not printed.

Minerals, phosphorus chemistries and nitrogen chemistries together make up the halogen-free flame retardants, and within that group the mineral hydroxides are the high-loading end.

ATH vs magnesium hydroxide (MDH)#

ATH is the right mineral for PVC, EVA, polyethylene and thermosets, and MDH takes over above about 200 °C (392 °F), because magnesium hydroxide stays intact to roughly 320 °C (608 °F) and tolerates a processing temperature about 110 °C higher. That difference is what puts MDH into polypropylene and polyamide compounds and keeps ATH out of them.

The trade-off runs the other way on heat absorbed per gram. MDH absorbs 1316 J/g against ATH's 1051 J/g, but carries less water, 31.0 % against 34.6 %. Natural brucite, CAS 1317-43-7, is the mined form of the same compound. Both minerals then face the same arithmetic in the compound: engineering plastics processed at 240 to 320 °C (464 to 608 °F) rule out ATH entirely, so the comparison only arises inside the 200 °C window where both are usable.

ATH vs boehmite#

Boehmite (AlO(OH), CAS 1318-23-6, EC 215-284-3) is the high-temperature aluminium mineral: it carries a single hydroxyl layer instead of three, dehydrates above ATH's onset and therefore survives nylon, PBT and lead-free-solder FR-4 laminate processing. It leaves the same alumina residue as ATH but releases less water per gram, so it buys thermal stability at the cost of cooling capacity.

Boehmite's exact decomposition onset, mass loss and density are not established in this reference and are left out of Table T8 rather than estimated. Boehmite survives nylon and PBT processing where ATH does not, which is the whole reason a formulator pays for it, and the substance has its own record at boehmite.

ATH vs huntite-hydromagnesite#

Huntite-hydromagnesite releases its volatiles in three stages instead of one: water from about 220 °C (428 °F), carbon dioxide from about 330 °C (626 °F) and a cement-like char at about 560 °C (1,040 °F). The natural blend of huntite, CAS 19569-21-2, and hydromagnesite, CAS 12072-90-1, loses 51 to 54 % of its mass on ignition at 1,000 °C (1,832 °F), more than either single hydroxide.

That staged release is the selling point and the complication: the compound gets protection across a wider temperature band, but the platelet morphology of huntite raises viscosity faster than the blocky particles of ATH. Huntite hydromagnesite releases water, then carbon dioxide, then forms a char, and the figures above come from LKAB Minerals data on its UltraCarb grades.

ATH vs halogenated flame retardants#

ATH trades loading for regulatory certainty: a brominated system reaches UL 94 V-0 at roughly a tenth of the loading, but every major brominated flame retardant on this site carries an SVHC listing, a POPs listing or both, and ATH carries neither. The numbers are stark: 5 wt% antimony trioxide with 10.7 wt% bromine gives UL 94 V-0 at 0.8 mm in HIPS, against 60 to 65 wt% ATH for the same rating class in thermoplastics generally.

Loading is the price of admission for mineral flame retardants, and it is paid in density, viscosity and elongation rather than in compliance risk. The ENFIRO project, EU FP7 grant 226563, concluded in 2012, placed ATH among the halogen-free options with good environmental and health profiles, while decaBDE and HBCD are Stockholm Convention pollutants and TBBPA carries a harmonised Carc. 1B classification from 1 September 2025.

Who Manufactures ATH? Grades and Suppliers#

ATH is produced by Huber Advanced Materials, which sells the Martinal, Micral and Hydral lines, and by Nabaltec, which sells Apyral. Huber completed the acquisition of Albemarle's Martinswerk business, which brought the Martinal ATH and Magnifin MDH lines with it, on 1 February 2016.

Five further trade names are recorded without an attributed producer and are listed as such rather than assigned to a company. Buyers should request the supplier's technical data sheet, the particle-size distribution and the surface-treatment type before comparing prices, because two grades with the same CAS number can differ by two orders of magnitude in median particle size. More producers and their locations are in the directory of flame retardant manufacturers and suppliers.

Table T9. ATH producers and brands.

ATH grades: precipitated, ground and surface-coated#

ATH grades differ on two axes: particle size, from 0.25 to 80 µm, and surface treatment, from untreated through fatty acid to vinyl silane and amino silane. ATH is sold in 3 grade families, listed below.

• Fine precipitated grades. Small particle size and high surface area, used in cable compounds and thermosets.
• Coarse ground grades. Large particle size, used as filler and in castings.
• Surface-coated grades. Vinyl silane for silane crosslinking, amino silane for thermoplastics, fatty acid for dispersion.

The full Martinal, Micral and Hydral ranges are listed on the Huber profile, where each grade carries its own median particle size and coating.

How Does ATH Fit into the Mineral Flame Retardant Family?#

ATH is the entry point to the mineral flame retardants, the class of metal hydroxides and carbonates that work by endothermic decomposition rather than by chemistry in the flame. Magnesium hydroxide, boehmite and huntite-hydromagnesite are its siblings in that class, and all four are separated by decomposition temperature rather than by mode of action.

The class boundary is visible in the dosage. A mineral hydroxide is used at 30 to 65 wt% while a brominated, phosphorus or nitrogen flame retardant works at 1 to 20 wt%, which means the mineral is a structural component of the compound and the chemical is an additive in the ordinary sense. At 30 to 65 wt%, ATH behaves like every other mineral in the guide to fillers for plastics, except in its purpose. No claim about the world market position of ATH is made on this page, because no dated tonnage or share figure is held in this reference.

Three aluminium minerals in plastics: ATH, boehmite and alumina#

Three aluminium minerals appear in plastics data sheets and only one of them is a flame retardant: ATH (Al(OH)3), boehmite (AlO(OH)) and alumina (Al2O3). ATH carries three hydroxyl groups, boehmite one, and alumina none at all.

Alumina, CAS 1344-28-1, EC 215-691-6, molecular weight 101.96 g/mol, is FCM substance 418, reference 34720, under Regulation (EU) No 10/2011, and it is bought as a thermally conductive and electrically insulating filler. Alumina conducts heat; ATH releases water. Confusing the two on a purchase order buys a filler with no fire performance at all.

Non-plastics uses of aluminium hydroxide (outside this site's scope)#

Aluminium hydroxide sold as an antacid, a vaccine adjuvant, a ceramics raw material or an artist's pigment extender is the same compound as ATH, but those uses fall outside this site's scope, which covers additives used in plastics. Paints, coatings, inks, paper chemicals, food and feed additives, cosmetics and pharmaceuticals are treated the same way across this reference.

The categories are named here only so that a reader who arrived on a pharmaceutical or ceramics query can see immediately that this page answers a different question. No dose, pharmacopoeia reference or medical statement appears on this page.

Is ATH banned or restricted anywhere?#

No: ATH is not restricted under REACH Annex XVII, is not on the REACH Candidate List, is not listed under the EU POPs Regulation (EU) 2019/1021 or the Stockholm Convention and is not restricted under RoHS Directive 2011/65/EU (status 23 September 2026). The restricted flame retardants are elsewhere in the family: decaBDE, HBCD, TBBPA, DBDPE and Dechlorane Plus all carry SVHC entries, and decaBDE, HBCD and Dechlorane Plus are Stockholm Convention pollutants. Bans and furniture standards by country are compared on flame retardant regulations.

Can ATH alone give a UL 94 V-0 rating?#

A UL 94 rating belongs to a compound at a stated thickness, not to an additive: in the Huber flexible PVC formulations, 45 to 100 phr ATH with 5 phr zinc borate reaches V-0 at 3 mm, and the patent literature puts 60 to 65 wt% as the general range for V-1 to V-0 in thermoplastics. Thickness changes the answer, since the V-0 criteria of 10 s per afterflame and 50 s total for 5 specimens are applied to a bar of a declared dimension. Match polymer, thickness and rating in the flame retardant selector.

What does ATH cost, and who supplies it in India and China?#

ATH is priced as a bulk mineral, by grade, particle size and surface treatment rather than by a single quoted number, and this site publishes a price only where a dated, sourced figure exists. No ATH price figure and no Indian or Chinese producer record is held in this reference, so none is printed here.

Price guides that do carry dated figures are collected under plastic additive prices, and regional sourcing runs through plastic additive manufacturers and suppliers in India, where regional producers are listed by state and product family.