Carbon fiber

Overview

Carbon-rich filaments produced from a precursor such as PAN or pitch and usually used in a composite system.

Feel and behavior

Stiff reinforcement rather than ordinary apparel softness.

Where you find it

Composites, sporting goods, vehicles and structural reinforcement.

Source and geography

Carbon fiber is made by heating a carbon-rich precursor fiber until almost everything except carbon has been driven off. Most commercial fiber starts from polyacrylonitrile (PAN) copolymer; mesophase pitch gives high-modulus grades, and lignin, cellulose and bio-based PAN are researched as renewable precursors. Production is capital- and energy-intensive. Beyond composites, carbon and oxidized PAN fibers are blended into flame-resistant knitted fabrics for firefighter station wear, a textile use distinct from structural reinforcement.

Worth knowing

• Large-tow carbon fiber with 48,000 or more filaments per bundle was developed to cut cost for wind energy and industrial parts rather than to improve performance.
• A review of carbon fiber life cycle studies found that where the fiber is made matters: the grid electricity mix shifted climate impact by several kilograms of CO2e per kilogram of fiber.

Types, grades and fabrics

Types and grades

Carbon fiber is specified by tow size and modulus class. 'K' counts thousands of filaments per tow, from 1K and 3K up to 12K, 24K and large tows of 48K to 50K; Toray lists its standard-modulus T300 in 1K, 3K, 6K and 12K tows and T700 in 6K, 12K and 24K. Standard-modulus fibers such as T300 have a tensile modulus near 230 GPa; intermediate- and high-modulus PAN grades and pitch-based ultra-high-modulus fibers trade strength or cost for stiffness. Product forms include continuous tow, unidirectional tape, woven fabric, non-crimp fabric, braided sleeve, prepreg with resin already applied, chopped and milled fiber, and nonwoven mats of recycled fiber.

Fabrics and products

Small tows such as 3K are woven into the plain and twill fabrics seen on bicycle frames, car trim and consumer goods, where the pattern is visible under clear resin. Larger 12K to 50K tows go into unidirectional tapes, non-crimp fabrics and pultrusions for wind turbine spar caps, pressure vessels and civil strengthening, where cost matters more than appearance. Braided sleeves form tubes such as fishing rods and hockey sticks. Outside composites, carbon fiber makes heating elements and conductive textiles, and oxidized PAN, an intermediate stage, is blended into flame-resistant fabrics.

Buying and care

How to judge quality

Buyers of fabric should ask for fiber grade and tow size, weave, areal weight in grams per square meter, sizing compatibility with the intended resin, and, for prepreg, resin system, cure schedule and out-life. For finished parts, laminate test data and the layup matter more than the weave on the surface: a glossy 3K twill can be a cosmetic layer over fiberglass or foam. Look for dry spots, pinholes, resin-starved areas, wrinkles and fiber misalignment. Red flags include 'carbon' products that are vinyl wraps or printed polyester, and strength claims without test data. Large tows cost less per kilogram but give coarser surfaces.

Care in detail

Clean composite products with mild soap and water, and avoid strong solvents that can attack the resin or clear coat. Follow torque specifications for clamps and fittings, because overtightening crushes tubes. After a crash or hard impact, have critical parts such as bicycle frames, forks or climbing gear inspected, since damage may not show on the surface. Protect clear-coated surfaces from prolonged sunlight, which yellows and degrades resin. Store dry fabric flat or rolled in a clean, dry place; prepregs are usually kept frozen and have limited working time at room temperature. Do not sand or cut composites without dust control.

Care at a glance

Use the manufacturer’s application-specific maintenance and handling instructions. Technical performance cannot be inferred from household laundry guidance.

Environmental and social footprint

Carbon fiber production is energy-intensive. A review of life cycle studies titled 'Bringing Light into the Dark' reported climate impacts of about 13 to 29 kg CO2e per kg of PAN-based carbon fiber in global scenarios and about 34 kg in a Chinese grid scenario, and estimated that renewable electricity plus process optimization could cut the impact by about 62 percent. In use, lighter vehicles and aircraft can offset some of this. End of life is the weak point: thermoset composites are mostly landfilled, and pyrolysis recovery works but reduced recovered fiber tensile strength by up to about 35 percent in one steam and air study.

Tradeoffs

Evaluate the specified grade, whole product, useful lifetime and realistic recovery route. A technical property does not establish a lower overall impact.

A useful question to ask: What exact material, product form and documented producer stand behind this name?

Science

Data sheet

Application-specific engineered material

Read the exact polymer, precursor and grade before comparing performance.

Structure and chemistry

Carbon fiber consists of graphene-like layers of hexagonally bonded carbon. In PAN-based fiber these layers form small, imperfectly stacked crystallites in a turbostratic structure, while pitch-based fibers develop longitudinally aligned graphitic crystals that give higher modulus. Alignment of layers along the fiber axis, interlayer spacing and crystallite size control stiffness and strength, and a skin-core difference inherited from stabilization can limit strength. Filaments are fine and uniform and are gathered into multifilament tows. The fiber is electrically conductive, very stiff in tension and strongly anisotropic, with weak transverse and compressive properties relative to its tensile strength.

From source to yarn

For PAN fiber, a wet-spun acrylonitrile copolymer precursor is first stabilized by heating in air under tension. Dehydrogenation, oxygen uptake and cyclization of nitrile groups turn the chains into a ladder-like, aromatized structure that will not melt; ladder formation accelerates above about 200 C, and multistage heating controls the exothermic reactions. The stabilized fiber is carbonized in inert gas at high temperature, for example 1,400 C with controlled draw in one study, and may be graphitized at still higher temperatures, such as 2,400 C in argon. The surface is then treated and sized before winding.

Performance in use

Carbon fiber gives very high stiffness and strength per unit weight and good fatigue resistance, but only inside a well-made composite, where the resin transfers load and the textile architecture sets directionality. It is brittle, with low strain to failure. Its conductivity is useful for electrodes and heating, but causes galvanic corrosion in bonded fiber-metal hybrids and short circuits from stray fibers. Machining, cutting and grinding composites releases dust: a study in a Japanese factory found carbon fiber fragments meeting the WHO respirable fiber definition, although concentrations were below the local limit set for asbestos-handling facilities.

How it is identified

Carbon fiber is black, lustrous and electrically conductive, which separates it from black-dyed glass or aramid. Burn tests are indicative only: carbon fiber glows but does not melt or flame in an ordinary burner, while the resin in a composite burns off. Microscopy shows smooth, fine, uniform filaments. Raman spectroscopy and X-ray diffraction characterize graphitic order, and scanning electron microscopy identifies respirable fragments in dust. Printed or woven 'carbon-look' polyester is common in consumer goods.

History

Timeline

1. 2016Electron-beam irradiation of polyacrylonitrile precursor fibers was shown to shorten the thermal stabilization step by about one quarter. [2]
2. 2021A review of lignin-based carbon fibers measured progress against a US Department of Energy target of 1.72 GPa strength and 172 GPa modulus, which few studies had approached. [3]
3. 2022A factory study in Japan found carbon fiber fragments meeting the WHO respirable fiber definition during cutting and grinding of carbon fiber reinforced plastics. [4]
4. 2024Pyrolysis followed by oxidation was reported as a route for recovering carbon fibers from waste composites. [5]

Modern carbon fiber grew through research into high-performance reinforcement. The textile architecture and resin are as important as the filament to the final composite.

The deeper record

PAN became the dominant carbon fiber precursor because stabilizing and carbonizing oriented PAN under tension preserved molecular orientation and gave strong filaments, while pitch routes served high-modulus niches. Aerospace, sporting goods, wind energy and automotive composites drove growth. Research now targets cheaper, lower-energy routes: melt-spinnable acrylonitrile copolymers, electron-beam irradiation that shortened thermal stabilization by about one quarter, microwave-assisted processing, and lignin-based fibers aimed at a US Department of Energy target of 1.72 GPa strength and 172 GPa modulus, which only a few studies have closely approached.

Labeling and law

Carbon fiber is mainly sold as composite reinforcement, and textile fiber labeling rules apply only when it is part of a regulated textile product; then the applicable generic name under 16 CFR 303.7 or Regulation (EU) No 1007/2011 must be checked. Strength and modulus grades are producer designations, and composite parts should be judged from laminate test data. Bio-based claims for lignin or bio-PAN carbon fiber need documentation of the renewable feedstock share.

This describes what rules and standards cover. It is not legal advice; jurisdiction, product form and current rule text control.

Frequently asked

What does 3K carbon fiber mean?

It means each tow contains about 3,000 filaments. The number describes the bundle size, not the grade or strength. Small tows like 3K make fine, even weave patterns favored for visible surfaces, while 12K and larger tows are cheaper per kilogram and used for thick structural parts.

Is carbon fiber stronger than steel?

Per unit weight, carbon fiber composites are far stiffer and stronger than steel in the fiber direction. Across the fibers and under impact they are weaker, and they fail without bending first, so good design orients fibers along the loads.

Can carbon fiber be recycled?

Yes, partly. Pyrolysis and solvent processes can remove the resin and recover fibers, which are usually chopped and reused in nonwovens, molding compounds or concrete. Recovered fibers are shorter and can be weaker than virgin fiber, so they rarely return to aerospace structures.

Sources

• Museum of Fine Arts, Boston: CAMEO materials reference
• Nanomaterials: Draw-induced structural optimization of PAN-based carbon fibers during high-temperature carbonization (2025)
• Materials: A methodology to enhance the stabilization process of PAN fibers by modeling and advanced characterization (2020)
• International Journal of Biological Macromolecules: Towards producing high-quality lignin-based carbon fibers, a review (2021)
• International Archives of Occupational and Environmental Health: Respirable fibers generated during cutting and grinding of carbon fiber-reinforced plastics (2022)
• Scientific Reports: Electron-beam irradiated polyacrylonitrile fibers to shorten thermal stabilization (2016)
• Toray Composite Materials America: Standard, intermediate and high modulus carbon fiber (producer page)
• Polymers (PMC): Bringing light into the dark, overview of environmental impacts of carbon fiber production and potential levers for reduction
• Polymers: High-efficiency carbon fiber recovery method and characterization of carbon fiber-reinforced epoxy/DDS composites (2022)
• Waste Management: Recovering carbon fibers from waste CFRPs via pyrolysis-oxidation (2024)
• Toray Composite Materials America: TORAYCA T300 standard modulus carbon fiber data sheet (producer)

Cite this page

Chaos. (2026). Carbon fiber. In Fibers of Earth: An independent textile atlas. https://www.hendrickresearch.com/fibers/materials/carbon/