Carbon fibre filament explained: is it worth it?

Carbon fibre filament is an ordinary 3D printing plastic, usually PLA, PETG or nylon, with short chopped carbon fibres mixed into it. The fibres make a printed part stiffer, more dimensionally stable and matte in appearance. They do not turn it into the carbon fibre of bike frames and racing cars, they do not always make it stronger, and they wear out a standard brass nozzle quickly. It is worth buying when you need rigidity or a clean technical finish, and it is the wrong choice when you need toughness.

What is actually in it

The carbon fibre in a bike frame is made of long continuous strands, laid in chosen directions and set in resin. The strength comes from the length and direction of those strands.

Carbon fibre filament is different. The fibres are chopped to a fraction of a millimetre so that they pass through a nozzle, and they make up a minority of the material; the rest is the base plastic. The proportion varies by brand and is often in the range of 10 to 20 per cent by weight, though not every manufacturer states it. The result behaves like a reinforced version of the base plastic, not like a carbon fibre laminate.

That is why the base matters more than the “CF”:

Carbon-fibre versions of ABS, ASA, PET and polycarbonate also exist and follow the same pattern.

Stiffer is not the same as stronger

This is the point most listings blur. Three different properties are involved:

• Stiffness is how much a part resists bending. Carbon fibre raises this clearly. A CF bracket flexes less than the same bracket in the plain plastic.
• Strength is how much load a part takes before it breaks. Along the printed lines, fibres can raise it somewhat. Between layers they generally do not help, and layer adhesion in a filled filament is often slightly worse than in the plain version.
• Toughness is how well a part survives a knock. Carbon fibre usually lowers it. Filled parts tend to crack rather than bend, and PLA-CF in particular is more brittle than plain PLA.

So a carbon fibre part is a rigid part, not an unbreakable one. If something keeps snapping, a tougher plastic is the fix, not a filled one. See the strongest 3D printer filament for how the materials compare.

What you gain

• Rigidity for the same shape and weight.
• Dimensional stability. The fibres reduce shrinkage as the plastic cools, so parts warp less and hold their size better. This is the main reason nylon-CF is so much easier to print than plain nylon.
• A matte, slightly textured surface that hides layer lines unusually well. Many people buy PLA-CF for the look alone.
• Cleaner overhangs and less stringing than the base plastic in many cases, most noticeably with PETG.

What it costs you

• A hardened nozzle is required. Carbon fibre is abrasive and wears a brass nozzle open, sometimes within a single spool. Fit hardened steel or another wear-resistant nozzle before you load it. See hardened vs brass nozzles.
• Wear elsewhere. Extruder gears and any PTFE tube in the filament path wear faster too. Printers sold as suitable for abrasive filament have hardened gears as well as a hardened nozzle.
• A bigger nozzle helps. The fibres can clog small nozzles. Many manufacturers recommend 0.4 mm as a minimum and 0.6 mm for reliable printing, and advise against 0.2 mm altogether. Check the spool's own guidance. See nozzle sizes explained.
• Brittle filament. The strand itself can snap on tight bends, which matters in long feed tubes and some multi-spool units. Printer makers publish which filled filaments their units accept.
• Price. CF grades cost noticeably more per kilogram than the plain plastic, and often come on smaller spools, so compare by price per kilogram.
• Limited colours. The fibres are black, so the range is black, greys and a few dark shades.
• Drying. A filled filament absorbs moisture just as its base plastic does. Nylon-CF must be dried before use and kept dry while printing; PETG-CF benefits from it. See do you need a filament dryer?

One handling note: sanding or cutting a carbon fibre print releases fine dust and loose fibres that can irritate skin and lungs. Sand wet where you can, wear a dust mask, and wipe the dust up rather than blowing it away.

What your printer needs

• PLA-CF: any printer that prints PLA, plus a hardened nozzle. No enclosure.
• PETG-CF: the same, at PETG temperatures.
• Nylon-CF: an all-metal hotend that reaches the temperature on the spool, hardened nozzle and gears, a dryer, and preferably an enclosure. See enclosed vs open-frame printers and nylon ranked by £/kg.

When it is worth it

• Yes: jigs, fixtures and tool holders that must not flex; drone and RC frames; camera and instrument mounts; long thin parts that would otherwise bend; enclosures and visible parts where you want a matte technical finish.
• Yes, nylon-CF specifically: functional parts that are loaded while warm, where plain nylon would be the choice if it did not warp.
• No: clips, hinges, snap-fits and anything that needs to flex or take impacts. Use plain PETG, nylon or PLA+.
• No: parts that fail from heat. PLA-CF in a hot car deforms just as PLA does.
• No: decorative prints in colour, or anything where the cost and nozzle change buy nothing.

For a first try, PLA-CF or PETG-CF with a hardened steel nozzle is the low-risk route: you find out whether you like the finish and the stiffness without taking on nylon's demands. Compare prices at PLA-CF ranked by £/kg and PETG-CF ranked by £/kg.

Questions people ask

What is carbon fibre filament?

Carbon fibre filament is a standard 3D printing plastic, usually PLA, PETG or nylon, with short chopped carbon fibres mixed in. The fibres are a minority of the material, often around 10 to 20 percent by weight depending on the brand. It prints stiffer, more dimensionally stable and with a matte finish, but it behaves like a reinforced plastic rather than like the continuous carbon fibre used in bike frames.

Is carbon fibre filament stronger than normal filament?

Carbon fibre filament is stiffer than normal filament, but not necessarily stronger. The chopped fibres make a part resist bending and hold its shape, and can add some strength along the printed lines. They do not improve the bond between layers and usually make the part more brittle, so a carbon fibre print cracks under impact more readily than the same part in the plain plastic.

Do you need a hardened nozzle for carbon fibre filament?

Yes, carbon fibre filament needs a hardened steel or other wear-resistant nozzle. Carbon fibre is abrasive and can wear a standard brass nozzle open within a single spool, which gradually ruins print accuracy. Extruder gears and PTFE tubing also wear faster, so printers designed for abrasive filament have hardened gears as well.

Can any 3D printer print carbon fibre PLA?

Almost any 3D printer that prints PLA can print carbon fibre PLA once a hardened nozzle is fitted. PLA-CF needs no enclosure and prints at ordinary PLA temperatures. A 0.4 mm nozzle is the usual minimum and 0.6 mm is often recommended, because the fibres can clog smaller nozzles.

What is the difference between PLA-CF, PETG-CF and nylon-CF?

The difference is the base plastic, which sets the heat resistance and difficulty. PLA-CF is the easiest to print but still softens at around 55 to 60 degrees Celsius. PETG-CF holds up to roughly 75 degrees and strings less than plain PETG. Nylon-CF is the engineering choice for warm, loaded parts, and needs drying, high temperatures and preferably an enclosure.

Is carbon fibre filament worth the extra cost?

Carbon fibre filament is worth the extra cost when a part must be rigid or needs a matte technical finish, such as jigs, drone frames, mounts and long thin parts. It is not worth it for clips, hinges and parts that take impacts, because it is more brittle than the plain plastic. It also costs more per kilogram and requires a hardened nozzle.

Why does carbon fibre filament have a matte finish?

Carbon fibre filament has a matte finish because the chopped fibres break up the smooth surface of the extruded plastic, so it scatters light instead of reflecting it. The slightly textured surface hides layer lines unusually well. Many people buy carbon fibre PLA mainly for this look, and the fibres also limit the colour range to black, greys and dark shades.