Carbon Fiber Reinforced Plastics: 3 Fiber Forms, Properties, Loading and Selection

Carbon fiber reinforced plastics (CFRP) are polymers reinforced with carbon filaments 5 to 10 µm across, made by carbonising a PAN, pitch or rayon precursor, and they reach a modulus of 150 to 250 GPa in civil-engineering composite grades, the highest stiffness of the 5 reinforcing fibres used in plastics. Carbon fibre enters a plastic in 3 forms, milled, chopped or continuous, and it acts as a conductive filler where glass insulates, so which form, which polymer and how much fibre does a compound need? The answer turns on 3 trade-offs that the sections below quantify wherever our sources allow: stiffness per unit weight against cost, conduction against insulation, and fibre length against ease of moulding.

Reinforcing fibres sit in the fillers and reinforcements group of the 43 families of plastic additives, and a reinforced plastic carries 15 to 30 wt% of fibre in the composition ranges published by Chea and co-workers in 2025, adapted from the product survey of John Hahladakis and colleagues at the University of Leeds (Journal of Hazardous Materials, 2018). Carbon fibre is the stiffest member of that group, and its record in our sources is narrow: density, single-filament strength, resistivity and producer data are not yet held, so each gap is named where it would appear.

This page defines carbon fiber reinforced plastic and separates the fibre from carbon black, carbon nanotubes and graphite, follows the fibre from precursor to sized filament, explains how it carries load and why it needs a sizing, then compares the 3 forms, the 4 properties that set it apart, the difference from glass fibre, the CF30 loading convention, 6 polymer routes, the effect on the rest of the additive package, the test methods, the regulatory record and the supplier chain. The comparison of all 5 fibres, glass, carbon, aramid, natural and basalt, is on reinforcing fibers for plastics, while every section below covers carbon only.

In brief:

• Filament diameter: 5-10 µm (0.005-0.010 mm)
• 3 precursors: PAN (polyacrylonitrile), pitch and rayon
• Oxidative stabilisation of PAN: about 300 °C in air, before carbonisation
• Modulus: 150-250 GPa in civil-engineering CFRP (a composite value), against 76.0 GPa for the E-glass filament

What Is Carbon Fiber Reinforced Plastic (CFRP)?#

Carbon fiber reinforced plastic is a thermoplastic or thermoset in which carbon filaments, with the aspect ratio of 20 to over 1,000 that defines reinforcing fibres, take over part of the mechanical load from the polymer, which makes the fibre a reinforcing additive rather than a filler. A reinforcement raises tensile strength and modulus because load passes from the matrix into the fibre by interfacial shear. The aspect ratio is the dividing line: wollastonite needles reach 5 to 30 and talc platelets 5 to 40, while reinforcing fibres such as glass, carbon and basalt start at 20 and run past 1,000. This page covers carbon fibre as an additive in plastic compounds and in the resin of thermoset composites; CFRP plates for strengthening concrete are a construction product and sit outside the scope of this site.

What is carbon fiber made of?#

Carbon fiber is made of carbon: it starts as an organic precursor fibre, polyacrylonitrile (PAN), pitch or rayon, that is heated until almost everything except the carbon has been driven off, leaving a black filament 5 to 10 µm across. The PAN precursor passes through oxidative stabilisation at about 300 °C in air before carbonisation, and that step turns a textile fibre into a heat-stable carbon skeleton. The filament is black, which limits the colour range of every compound that contains it.

Our source library holds no verified carbon content in percent for a commercial fibre, so this page states the composition qualitatively. Since the finished part is fibre plus polymer, which name belongs to which: CFRP, CFRTP or a carbon-filled compound?

CFRP, CFRTP and carbon-filled compounds: what the terms mean#

CFRP names the finished material, polymer plus carbon fibre, while "carbon fiber" names only the filament, although car and consumer usage often calls a CFRP part "carbon fiber" as well. The same material also appears as carbon fibre reinforced polymer, carbon fiber composites or carbon-filled plastic, and the spelling splits by region into "fiber" in the US and "fibre" in UK and international usage. Four labels describe carbon fibre in a plastic, and they differ by matrix and by form.

• CFRP: carbon fiber reinforced plastic or polymer, the umbrella term and the usual name for thermoset laminates
• CFRTP: carbon fiber reinforced thermoplastic, the thermoplastic branch, covering tapes, organosheets and compounds
• Carbon-filled compound: a thermoplastic pellet with chopped or milled fibre for injection moulding, named by fibre content as CF10, CF20 or CF30
• Carbon fiber: on its own, the filament; in car and consumer usage, often the finished CFRP part

Is carbon fiber a plastic?#

No: carbon fiber is a carbon filament, not a plastic, and it becomes part of a plastic only when it is embedded in a polymer matrix as CFRP. The confusion has a chemical origin, since the PAN precursor is itself a polymer before carbonisation removes almost everything except the carbon.

Carbon fiber vs carbon black, carbon nanotubes and graphite#

Four carbon additives go into plastics, carbon black, carbon nanotubes, graphite and carbon fibre, and carbon fibre is the only one of them that reinforces, because it is the only one supplied as a filament long enough to carry load. The 4 carbon additives differ in form, function and regulatory position, as Table 2 shows.

Table 2. The 4 carbon additives used in plastics.

Absence from a list in this table is a statement about the sources checked, not a prohibition.

The CLP entry that classifies multi-walled carbon nanotubes is defined by tube diameter, length and aspect ratio, and carbon fibre is not named in it. Neither that classification nor the Proposition 65 listing of carbon black transfers to carbon fibre, because each entry names its own substance. The consumer searches for "black and carbon fiber" refer to the woven look of finished CFRP parts, not to a carbon additive.

How Is Carbon Fiber Made from PAN, Pitch and Rayon?#

Carbon fiber is made by spinning a precursor fibre such as polyacrylonitrile, stabilising it in air at about 300 °C, carbonising it at a much higher temperature without oxygen, and finishing it with a surface treatment and a sizing. The 3 precursors named in our sources, PAN, pitch and rayon, differ in what the source library records for each, as Table 1 shows.

Table 1. The 3 carbon fibre precursors.

Empty cells mean our source library holds no verified value, not that none exists.

Carbon fibre is produced in 4 steps.

1. Spin the precursor into a continuous fibre.
2. Stabilise the fibre in air, PAN at about 300 °C, so that it survives the heat that follows.
3. Carbonise it at high temperature without oxygen, which drives off almost every element except carbon.
4. Treat the surface and apply a sizing, so that the fibre bonds to its matrix and survives handling.

Stabilisation is the only step in this sequence for which our sources hold a temperature. The carbonisation temperature, the surface-treatment method, the share of each precursor in world production and the production history are not held in our source library, so the list describes the sequence rather than a plant recipe.

How Does Carbon Fiber Reinforce a Polymer?#

Carbon fiber reinforces a polymer by shear transfer: the matrix strains, shear stress builds along the fibre surface, and the far stiffer carbon filament takes over the load, which is why carbon composite grades reach 150 to 250 GPa where the E-glass filament itself stops at 76.0 GPa. The Halpin-Tsai equations, published by Halpin and Kardos in Polymer Engineering and Science 16 (1976) 344-352, describe how the modulus of a short-fibre composite rises with fibre content and aspect ratio. Carbon brings the highest fibre stiffness into that relationship, and 3 carbon-specific consequences follow from it.

Load transfer and the 5 to 10 µm filament#

A carbon filament carries its full share of load only above a critical length, and because that length scales with fibre diameter, the 5 to 10 µm carbon filament needs less length to load fully than a coarser fibre with the same strength and the same interface. Critical length also depends on fibre strength and interfacial shear strength, so the comparison with basalt fibre, the coarser reference at 10 to 20 µm, holds only when those two factors are equal.

Fibre length falls in the extruder and again in the moulding machine, so the length surviving in the part, not the length bought, decides how much of the carbon's stiffness and strength the part uses. Long-fibre pellets of 10 to 12 mm keep 6.35 mm (0.25 in) or more of fibre in the part, but those data are recorded for glass, and no surviving-length value for carbon is held in our source library. So what makes the interface strong enough for that shear to build up at all?

Why carbon fiber needs a sizing rather than a silane coupling agent#

Carbon fiber needs a sizing matched to its matrix because the silane coupling agents that bond glass fibre are the wrong tool for carbon: the silane supplier Gelest lists graphite and carbon black among the surfaces on which silanes are ineffective. Glass works differently. 3-Aminopropyltriethoxysilane (APTES, CAS 919-30-2) and 3-glycidoxypropyltrimethoxysilane (GLYMO, CAS 2530-83-8), the silane coupling agents in glass-fibre sizes, bond through the surface hydroxyl groups of glass, and glass leaves the bushing carrying 0.5 to 2.0 wt% of a size made of film former, silane and lubricant.

Graphite and carbon black, the two carbon surfaces Gelest names, are the closest documented relatives of the carbon-fibre surface. Treating carbon fibre as the same class of surface is a reasoned inference rather than a measured result, because carbon fibre does not appear on the Gelest list itself, and a carbon surface does not offer hydroxyl groups in the same way that glass does.

The sizing chemistry applied to carbon fibre and its level on the fibre are not held in our source library, so no size type or percentage is stated here; the glass-fibre value of 0.5 to 2.0 wt% does not transfer. The same gap applies to the surface treatment that precedes sizing, whose method is not recorded either.

The choice of coupling agent therefore splits by fibre: silanes for glass, maleated polyolefins for glass, cellulose and polyamide end groups in polypropylene, and a matrix-matched sizing for carbon. Which coupling agent suits which filler and fibre is compared on coupling agents for filled and reinforced plastics.

What carbon fiber costs you: anisotropy, abrasion and unwanted conductivity#

Carbon fiber is bought with 4 penalties, anisotropy, tool wear, electrical conductivity where the part must insulate, and cost, and each is a specification decision rather than a defect. The 4 penalties of carbon fibre are listed below.

• Anisotropy and warpage: short fibres align with the flow, so shrinkage differs along and across it, and the part warps when the difference is large
• Wear on the screw, barrel and tool: abrasion of processing steel rises with filler hardness and with loading
• Unwanted conductivity: a carbon-filled part cannot be used where it must insulate, which removes it from most connector and switchgear duty that glass-filled nylon serves
• Cost: carbon fibre is bought for stiffness per unit weight, not on price, and no price value is held in our source library, so no ratio to glass is given

What Are the 3 Forms of Carbon Fiber Used in Plastics?#

The 3 forms of carbon fiber used in plastics are milled fibre, chopped fibre compounded into injection-moulding pellets, and continuous fibre in tapes, fabrics and laminates, and the form decides how much fibre length, and so how much of the fibre's strength, survives into the part. Table 3 compares the 3 forms in order of rising fibre length.

Table 3. The 3 forms of carbon fibre in plastics.

Long-fibre pellets, 10 to 12 mm long with the fibre running the full pellet length, sit between chopped and continuous fibre and are covered on long fiber thermoplastics (LFT), where the recorded data are for glass. The 3 forms here therefore cover the routes our sources document for carbon, and the order milled, chopped, continuous is kept in every list and table on this page.

1. Milled carbon fiber#

Milled carbon fiber is carbon filament ground to a short, powder-like length, used where a compound needs the conductivity, stiffness or wear behaviour of carbon with a smoother surface and easier flow than chopped fibre gives. Our sources list milled carbon fibre as a carbon additive in its own right, next to carbon black, graphite, graphene and carbon nanotubes, because at that length it behaves closer to a filler than to a reinforcement.

Milled fibre still carries the 2 conduction properties of carbon, electrical and thermal, which is why it appears in conductive and wear compounds rather than in structural ones. No length value for milled carbon fibre is held in our source library, so the surface and flow advantages stated here are qualitative.

2. Chopped carbon fiber for injection-molding compounds#

Chopped carbon fiber is the form inside injection-moulding pellets such as PA66 CF30 or PEEK CF30: the cut strand is fed into the polymer melt on a twin-screw extruder and leaves it as short fibres held in a pellet. PEEK and the wider PAEK family carry carbon fibre as one of their main additives, alongside glass fibre, PTFE and graphite, and the grade name always states the fibre content by weight. The fibres align with the flow when the pellet is moulded, so a chopped-fibre part is stiffer along the flow than across it.

Fibre is fed downstream during plastic compounding rather than into the main hopper, so it spends the least time under shear, and twin-screw compounding with a side feeder is the standard route for that reason. No attrition percentage is given here, because the size of the length loss is not verified in our sources.

3. Continuous carbon fiber: tapes, fabrics and laminates#

Continuous carbon fiber keeps its full length as tape, fabric or laminate, and it is the form behind the 150 to 250 GPa modulus quoted for civil-engineering CFRP, because no compounding step shortens it. The strength and modulus values in our sources, about 3 GPa and 150 to 250 GPa, are composite values for this form, which is why every comparison on this page carries the qualifier "civil-engineering CFRP". The matrices and processes used for continuous carbon laminates are not yet held in our source library, so they are not listed here.

What Are the Properties of Carbon Fiber Reinforced Plastics?#

Carbon fiber reinforced plastics combine 4 properties that set them apart from glass-reinforced grades: very high stiffness, stiffness per unit weight, electrical conduction and thermal conduction. Table 5 lists the values our sources hold for each property and names the gaps.

Table 5. Properties of carbon fibre and CFRP in our source library.

Composite values are for civil-engineering CFRP, not for a filament or an injection-moulded compound.

Stiffness and strength#

Stiffness is what carbon fibre is bought for: civil-engineering CFRP reaches a modulus of 150 to 250 GPa, roughly 2 to 3 times the 76.0 GPa of the E-glass filament, while its strength of about 3 GPa is in the same range as E-glass at 3,445 MPa. The carbon values are composite values for civil-engineering grades and the glass values are filament values, so the comparison understates carbon at the filament level. A composite carries the fibre diluted by its matrix, while a filament value describes the fibre alone, and the two cannot be set side by side without that correction.

Strength therefore stays the open half of the comparison. S-2 glass reaches 4,890 MPa and 85.5 GPa as a filament and basalt fibre 2.8 to 3.1 GPa and 85 to 87 GPa, so carbon's lead on modulus holds even against filament values, while a strength ranking, like the modulus classes of commercial grades, would need single-filament carbon data that our source library does not yet hold.

Density and weight#

Carbon fibre is chosen on stiffness per unit weight, but no density value for carbon fibre is held in our source library, so the weight saving against E-glass at 2.58 g/cm3 is not quantified on this page. The glass compositions in our sources run from 2.46 g/cm3 for S-2 glass to 2.58 g/cm3 for E-glass, and basalt sits at 2.67 g/cm3. Part-level claims that compare a carbon composite with steel or aluminum by weight are not repeated here, because they describe finished parts, not the fibre.

Is carbon fiber conductive? Electrical conductivity and EMI shielding#

Carbon fiber is used as an electrically conductive filler: it is one of the fillers, with carbon nanotubes, conductive carbon black, graphene and stainless-steel fibre, that turn an insulating plastic into an antistatic, static-dissipative or EMI-shielding compound once enough filler touches to form a continuous network. That network forms only above the percolation threshold, the filler content at which the particles or fibres connect into an electron-conducting path, and the threshold falls as aspect ratio rises. Carbon fibre is compared with CNT and conductive carbon black on conductive additives and fillers, the page that owns conductive compounding in general.

Unfilled polyethylene and polypropylene measure 1e15 to 1e16 ohm, anything above 1e14 ohm counts as insulative, and the antistatic band runs from 1e9 to 1e13 ohm, in the surface resistivity classes Ampacet uses. ASTM D257 is the method for those classes, and ASTM D4496 replaces it for moderately conductive materials. No resistivity value for carbon fibre or for a carbon-fibre compound is held in our source library, so this page gives the classes, not a carbon-fibre number, and no compound is assigned to a class here.

EMI shielding effectiveness is expressed in decibels, where 20 dB blocks 99 % of the incident radiation and 40 dB blocks 99.99 %, and a conductive enclosure reaches those levels only when its filler network is continuous. Shielding compounds and their decibel targets are covered on EMI shielding plastics; no shielding value for a carbon-fibre compound is held in our sources, so none is stated.

Thermal conductivity and heat resistance#

Carbon fibre raises the thermal conductivity of a plastic without keeping it electrically insulating, which places it with graphite and metal flakes and sets it apart from boron nitride or aluminium nitride, which conduct heat and insulate. That distinction decides the filler for electronics housings and heat sinks: a part that must spread heat and insulate at the same time takes hexagonal boron nitride, aluminium nitride or alumina, while a part that may conduct can take carbon fibre or graphite.

The canonical review of thermally conductive polymer composites, by Chen, Ginzburg, Yang and co-workers in Progress in Polymer Science 59 (2016) 41-85, is the standard reference for the filler classes behind that choice. Boron nitride, aluminium nitride and graphite are compared on thermally conductive fillers; no thermal conductivity value in W/(m·K) for carbon fibre or a carbon compound is held in our source library.

Carbon fibre is a standard filler in PEEK, a polymer that melts at 343 °C and is processed above 340 °C, so the heat limit of a carbon-filled part is normally set by the polymer, not by the fibre.

Carbon Fiber vs Glass Fiber Reinforced Plastics: What Is the Difference?#

Carbon fiber reinforced plastics are stiffer than glass fiber reinforced plastics, 150 to 250 GPa in civil-engineering CFRP against 76.0 GPa for the E-glass filament, and they act as conductive fillers where glass insulates, while glass keeps the advantages of lower cost and an EU food-contact listing. Whether CFRP is also stronger depends on the grade: our source library holds strength for carbon only as a composite value of about 3 GPa, against 3,445 MPa for the E-glass filament, so it does not support a general strength ranking. Glass types, sizing silanes and the GF grades are covered on glass fiber reinforced plastics, and Table 4 sets the two fibres against each other on 10 criteria.

Table 4. Carbon fiber vs glass fiber reinforced plastics on 10 criteria.

Carbon strength and modulus are composite values for civil-engineering CFRP; glass values are filament values. No price is given for either fibre because none is held in our source library.

The choice between carbon fibre and fibreglass follows the property that decides the part. Carbon is the choice where stiffness per unit weight or conduction decides, as in stiff, light housings, wear parts and antistatic components; glass is the choice where insulation, cost or food contact decides, as in connectors, switchgear and food-contact parts. A part that must insulate should stay glass-filled, whatever the stiffness target.

Carbon fiber vs aramid and basalt fiber#

Against the other high-performance fibres, carbon is the stiffest even on composite values: basalt reaches 85 to 87 GPa at 2.67 g/cm3 with a coarser 10 to 20 µm filament, and aramid is defined by its chemistry, at least 85 % of its amide links attached to two aromatic rings, rather than by a published modulus. That aramid definition dates from the US Federal Trade Commission in 1974 and ISO in 1977, the aramid polymer carries CAS 24938-64-5, and world para-aramid capacity stood at 41 kt per year in 2002. Para- and meta-aramid grades, and the wear compounds in which aramid and carbon fibre both appear, are covered on aramid fibres in plastics.

Claims on comparison pages that put aramid's strength level with carbon's, or its modulus between glass and carbon, are not supported by values in our sources and are not repeated here.

Basalt fibre is the mineral alternative: it reaches 2.8 to 3.1 GPa tensile strength and 3.15 % elongation at break as a filament, contains more than 46 % silica with a low iron content, and lands close to S-2 glass in stiffness rather than close to carbon. Its composition and the comparison with E-glass are on basalt fiber reinforcement.

How Much Carbon Fiber Does a Compound Contain?#

Reinforced plastics carry 15 to 30 wt% of fibre in the composition ranges of Chea and co-workers (2025), and carbon-fibre grades are named on the same weight basis, so a PA66 CF30 pellet holds 30 wt% carbon fibre. That 15 to 30 wt% band describes reinforced plastics as a class, glass included; a loading range measured on carbon-fibre compounds alone is not held in our source library, so no narrower carbon range is published here. The loading inside a grade still follows the target property, and 3 factors set it.

• Stiffness target: modulus rises with fibre content and with aspect ratio, as the Halpin-Tsai equations of Halpin and Kardos (1976) describe
• Conductivity target: the conductive network forms only above the percolation threshold, so a grade sold for antistatic or ESD duty needs enough fibre to connect
• Flow and surface: every extra percent of fibre costs flow length in the mould and surface finish on the part

What does CF30 mean?#

CF30 means the compound contains 30 wt% carbon fibre, so a PEEK CF30 pellet is 70 wt% PEEK and 30 wt% carbon fibre by weight, not by volume. The convention is the same one that produces GF30 for glass, and it always counts weight in the finished compound. CF30 and GF30 do not hold the same fibre volume, because the fibre volume depends on the fibre density, and no carbon-fibre density is held in our source library to calculate it.

Which Polymers Are Reinforced with Carbon Fiber?#

Carbon fiber reinforces engineering and high-performance thermoplastics, including polyamide, PEEK and PPS, as well as polypropylene, thermoset epoxy composites and 3D-printing filaments. Table 6 lists the 6 polymer routes with the temperatures and carbon-fibre records our sources hold for each.

Table 6. Polymers reinforced with carbon fibre and what our sources record.

An empty cell means our source library holds no verified record, not that the combination is unused.

Carbon-fiber nylon (PA6 and PA66)#

Carbon-fiber nylon is a PA6 or PA66 compound in which carbon fibre replaces glass to gain stiffness per unit weight, at the cost of the electrical insulation that keeps glass-filled nylon in connectors and switchgear. The matrix still needs the stabilization of any polyamide compound, and the glass route sets the reference for it. Heat stabilizers, flame retardants and grades of the glass route are covered on glass-filled nylon.

The one polyamide system with carbon fibre recorded in our sources is a recycled PA6/PP blend reinforced with carbon fibre, in which Joncryl ADR-4368-S acts as a chain extender. Joncryl ADR-4368 has a molecular weight of about 6,800 g/mol, an epoxy equivalent weight of 285 g/mol and about 9 epoxy groups per molecule, so each molecule offers about 9 reactive sites for the polymer chain ends that degraded during the first life of the material. The polyamide phase keeps its copper-halide heat stabilization, Cu at 0.001 to 0.03 wt% with 0.1 to 5 wt% halide, and the compound is processed in the 240 to 320 °C window recorded for engineering polymers such as PA66.

PEEK, PPS and other high-performance polymers#

PEEK is the clearest example of a polymer built around carbon fibre: it melts at 343 °C and is processed above 340 °C, which rules out organic additives and leaves carbon fibre, glass fibre, PTFE and graphite as its main additives. Its glass transition sits at 143 °C, and its processing window leaves only highly stable additives in the formulation. The full PEEK and PPS package is on additives for high-performance polymers, which covers the stabilizers that survive those processing temperatures.

Carbon fibre also appears with PTFE and graphite in PEEK and PAEK wear compounds, where fibre reinforcement raises stiffness and creep resistance and changes how the surface abrades. PPS, which serves continuously up to about 240 °C, is recorded in our sources with glass and mineral reinforcement, and no carbon-specific value for PPS is held in our source library.

Carbon-fiber polypropylene#

Carbon-fiber polypropylene is the hardest of the common carbon compounds to couple, because polypropylene has no reactive groups and the maleated-PP route that bonds glass works through surface chemistry that carbon does not share in the same way. In glass-filled PP, the succinic anhydride groups of maleated PP react with the Si-OH groups of the glass, while the PP backbone entangles with the matrix. The maleated-PP route is set out on glass-filled polypropylene.

The same anhydride groups also react with the OH groups of cellulose and the amine end groups of polyamides, which is why maleated PP couples wood and natural fibres as well as glass. A carbon surface offers neither of those groups in the same form, and no coupling study for carbon fibre in polypropylene is held in our source library.

The one recorded PP-containing carbon system is the recycled PA6/PP blend reinforced with carbon fibre and chain-extended with Joncryl ADR-4368-S, in which the polyamide phase supplies the reactive end groups that PP lacks. Stabilizers and nucleants for the matrix are on additives for polypropylene.

Epoxy and other thermoset CFRP composites#

Thermoset CFRP is carbon fibre laid up as fabric or tape in a resin such as epoxy and cured into a laminate, the form behind the 150 to 250 GPa quoted for civil-engineering CFRP. The resin side of that laminate carries its own additive package of tougheners, fillers, UV stabilizers and flame retardants. The resin-side package is on additives for epoxy resins and composites, which treats the laminate as a plastic rather than as a structural product.

Two additive families touch the laminate directly: tougheners for epoxy, which reduce the brittleness of the cured resin, and release agents that free the cured part from its tool.

Release is the step that every laminate tool repeats. Semi-permanent release coatings for laminate tools are on mold release agents for composites, which covers fiberglass, epoxy and SMC/BMC tooling.

Curing agents and hardeners are outside the scope of this site, since they build the polymer rather than modify it.

Carbon-fiber filaments for 3D printing#

Carbon-fiber 3D-printing filaments are chopped carbon fibre compounded into a printable polymer, and the fibre goes through a second extrusion in the printer nozzle, so its length in a printed part falls again after compounding. Our source library holds no carbon-fibre filament record, so this section states no loading, no printed-part property and no conductivity class for carbon filaments; whether a printed part conducts would depend on loading and fibre continuity.

The filament data our sources do hold concern glass-filled nylon filament and a PLA filament additive study (Namhongsa and co-workers, Polymers, 2025), neither of which involves carbon. Filament packages, carbon and glass alike, are on additives for 3D printing filaments.

How Does Carbon Fiber Change the Rest of the Additive Package?#

Adding carbon fiber changes 5 other parts of the formulation: the antistatic package, the wear package, chain extension in recycled grades, heat stabilization of the matrix and the colour range. The 5 changes are listed below, each with the additive family it touches.

• Antistatic and conductive additives: carbon fibre can make a separate antistat unnecessary in a conductive grade, since it is itself a conductive filler
• Wear additives: PEEK and PAEK wear grades combine carbon fibre with PTFE and graphite; PTFE and graphite are compared on tribological additives
• Chain extenders: Joncryl ADR-4368-S re-links recycled PA6/PP reinforced with carbon fibre; Joncryl ADR grades are profiled on chain extenders for polymers
• Heat stabilizers: the PA matrix still needs its copper-halide system, Cu 0.001-0.03 wt% with 0.1-5 wt% halide
• Colorants: a carbon-filled grade is black, so light colours are not available and pigment choice narrows to black and dark shades

The wick effect that raises flame-retardant demand in glass-filled polyamide is documented for glass in our sources, not for carbon fibre, so no flame-retardant adjustment for carbon grades is stated here.

How Are Carbon Fiber Compounds Tested?#

Carbon fibre compounds are tested with the same mechanical standards as any reinforced plastic, ISO 527 tensile, ISO 179 or ASTM D256 impact and ISO 75 heat deflection temperature, plus surface and volume resistivity to ASTM D257 or IEC 62631-3, which glass grades rarely need. Table 7 maps 7 properties to their methods and standards, with a note on what changes for carbon grades.

Table 7. Test methods for carbon fibre compounds.

Ashing to ASTM D5630-22 measures an inorganic residue of 0.01 % and above in materials stable to 900 °C, by procedure A (5 to 50 g in a muffle furnace) or procedure B (2 to 10 g, rapid ash), and it excludes halogenated and fluorinated polymers; whether carbon fibre survives that ashing step is not established in our sources, so no fibre-content method for carbon compounds is given here. Every method named in this section is indexed under testing plastic additives.

What Is the Regulatory and Health Status of Carbon Fiber in Plastics?#

Carbon fibre has a thin regulatory record compared with glass: it has no entry on the EU Union list of Regulation (EU) No 10/2011 in the sources checked and no United States food-contact citation in our sources, while glass fibre is listed as FCM 38. "No entry in the sources checked" is a statement about those sources, not a prohibition, and it is used in that sense throughout this section. Glass fibre, carbon black and graphite each have a defined position, and the 2 sections below show where carbon fibre stands next to them.

Food contact: no Union list entry for carbon fiber#

No Union list entry for carbon fibre appears in Regulation (EU) No 10/2011 in the sources checked, which leaves a food-contact carbon compound without the route that glass fibre has through FCM 38, and the graphite (FCM 521) and carbon black (FCM 411) entries do not cover a fibre. Glass fibers are listed as FCM 38 (Ref 55520) without a specific migration limit, so the generic SML of 60 mg/kg and the overall migration limit of 10 mg/dm2 apply to them. How the Union list works, and what an absence from it means, is explained on EU 10/2011.

Graphite is authorised as an additive under FCM 521 (Ref 58320) without an SML, and carbon black under FCM 411 with a maximum use level of 2.5 % w/w in the polymer; both entries name their own substance. Carbon nanotubes and other nanoforms can be used in EU food-contact plastics only if explicitly authorised (Article 9(2)). A food-contact application of carbon fibre therefore needs its own assessment.

The United States position follows the same pattern. 21 CFR 177.2410 lists glass fiber, asbestos fiber, diatomaceous earth, mica and carbon black as adjuvants in phenolic moulded articles, and carbon fibre is not among them; no other 21 CFR citation for carbon fibre is held in our sources. Every 21 CFR section that touches an additive is mapped on FDA food contact rules.

A listing with conditions is never an approval of a compound, and the absence of a listing is never a ban, so neither "FDA approved" nor "banned" describes carbon fibre.

REACH, CLP and the carbon nanotube entry#

The one carbon entry in the EU harmonised classification that a reader may connect with carbon fibre covers multi-walled carbon nanotubes, classified Carc. 1B and STOT RE 1 from 1 May 2026 for tubes 30 nm to 3 µm across, and carbon fibre is not named in it. The entry, index 006-104-00-2 in Annex VI of Regulation (EC) No 1272/2008, was added by Delegated Regulation (EU) 2024/2564 (ATP22) and covers multi-walled carbon tubes with a diameter of 30 nm or more and below 3 µm, a length of 5 µm or more and an aspect ratio above 3:1, classified Carc. 1B H350i and STOT RE 1 H372 (lung, inhalation). Annex VI entries and the ATP calendar are on CLP classification of plastic additives.

The filament diameter of carbon fibre, 5 to 10 µm, is larger than the entry's upper limit of 3 µm. That comparison explains why the entry does not name carbon fibre; it says nothing about the hazards of carbon-fibre dust, which the entry does not assess.

The REACH registration status, the CLP self-classification and any IARC or Proposition 65 entry for carbon fibre are not held in our source library, so none is stated here; dust from cutting and machining carbon composites is an occupational hygiene question for the plant's own risk assessment. Registration duties for fibres and sizings are explained on REACH and plastic additives.

Who Makes Carbon Fiber for Plastics?#

A carbon-fibre compound passes through 3 supplier layers, the fibre producer, the compounder that combines fibre and polymer, and the supplier of the sizing and co-additives, and a moulder usually buys from the middle layer by grade name, such as PA66 CF30. The fibre decision is then already made inside the compound, so the compounder's data sheet is the document that carries the fibre content, the polymer and the tested properties. Compounders and additive producers are profiled in the directory of plastic additive manufacturers and suppliers.

No carbon-fibre producer is named on this page because our source library holds no verified record for one, the same position the reinforcing fibre hub takes; no market size, tonnage or price is given for the same reason. Buyers should compare carbon compounds by fibre content, polymer and the tested property, not by the brand of the fibre inside.

─── The sections below cover related but broader questions, including construction products and recycling, that sit outside the core definition, forms, properties and selection guidance above. ───

Where Carbon Fiber Reinforced Plastics Go Beyond Compounding#

Most of what ranks for "carbon fiber reinforced plastic" is about finished composite parts, from concrete strengthening plates to aircraft structures, and this site covers only the part of that story that is a plastic and its additives.

CFRP in construction, aerospace, automotive and sports goods (mostly outside the scope of this site)#

CFRP plates and wraps for strengthening concrete are construction products and are outside the scope of this site, even though the only CFRP strength and modulus values in our sources, about 3 GPa and 150 to 250 GPa, come from them. Aerospace structures, car parts and sports goods made of CFRP are plastics, so they are in scope in principle, but our source library holds no application data for them, so they are named here as the subject of the wider search results rather than described.

Car parts are plastics, and their full additive package is on additives for automotive plastics, which treats a vehicle part as a plastic compound rather than as a finished component.

Can carbon fiber reinforced plastics be recycled?#

Thermoplastic carbon compounds can be reground and remoulded, but the fibre shortens at every melt step, so a recycled carbon compound is weaker than virgin material at the same fibre content.

What fibres do to a recycling stream is set out on how additives affect plastic recyclability, including the effect of fibre length and filler on sorting and reprocessing.

The documented recycled carbon system in our sources is the recycled PA6/PP blend reinforced with carbon fibre, in which Joncryl ADR-4368-S re-links the degraded chains. Recovering fibre from thermoset CFRP laminates is a separate process route and is not described here because our source library holds no verified data for it.

Regrind also needs its stabilizer package rebuilt, because the first life of the material and the second melt step consume part of the original antioxidants and heat stabilizers. Restabilization of regrind is covered on additives for recycled plastics, where the same rules apply to carbon-filled and glass-filled recyclate.

Carbon fiber FAQs#

Three more questions that searchers ask about carbon fibre are answered below.

What is carbon fiber reinforced plastic used for?#

Carbon fiber reinforced plastic is used where stiffness per unit weight, electrical conduction or wear resistance decides: in PEEK and polyamide compounds, in antistatic, ESD and EMI-shielding parts, in wear compounds with PTFE and graphite, and in thermoset composite laminates.

What are the disadvantages of carbon fiber reinforced plastic?#

The disadvantages of carbon fiber reinforced plastic are anisotropy, tool wear during processing, electrical conductivity where a part must insulate, cost, and a thin food-contact record, since carbon fibre has no EU Union list entry in the sources checked.

Is carbon fiber a metal?#

No: carbon fiber is a non-metallic filament made by carbonising an organic precursor such as PAN, although it is used as a conductive filler, which is the property that makes people ask. The question arises because electrical conduction is usually associated with metals, and carbon fibre conducts without any metal content.

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Every figure on this page is checked against primary sources; see our methodology and fact-checking process.

Byline: PlasticAdditives.net Editorial Team

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