Nylon and Carbon Fibre Parts

This is where FDM stops being a hobby process. Nylon and fibre-filled filaments make parts that go into machines and stay there. They also cost more, print harder and demand more from the design. Worth knowing when that trade is worth making — and when it plainly is not.

Nylon: tough, not stiff

Nylon (polyamide — PA6, PA12 and friends) is the tough one. Where PLA snaps and PETG bends, nylon absorbs. It takes repeated impact, it flexes without cracking, it survives fatigue, and it has genuinely good abrasion resistance and a low friction coefficient.

That makes it the material for gears, bushes, bearings, latches, living hinges, cable guides, wear strips — anything that rubs, cycles or gets hit. It also holds up to oils, fuels and solvents that would craze other plastics, which is why it belongs in industrial machine spares.

Its weaknesses are two:

• It is not stiff. A nylon bracket flexes more than a PETG one. Toughness and stiffness are different properties and nylon trades one for the other.
• It drinks water. This is the real problem. Nylon absorbs moisture from the air, and a wet part is softer, weaker and dimensionally larger than a dry one. A nylon part left out in a damp workshop keeps changing. It prints badly wet too — steaming filament makes a foamy, weak part — so it has to be dried before printing and often kept dry during it.

Adding carbon fibre

Chopped carbon fibre — short strands, not woven cloth — mixed into the plastic changes it considerably:

• Much stiffer. This is the headline. CF-filled nylon is dramatically less bendy than plain nylon and gets close to the stiffness of much harder plastics.
• Far less warping and shrinkage. The fibres restrain the plastic as it cools. For a big, flat, dimensionally fussy part this is often the main reason to use it, not the strength — see do 3D printed parts shrink.
• Less moisture sensitivity, because there is less nylon.
• Better heat resistance in the stiffness sense.
• A lovely matt black finish that hides layer lines better than any plain plastic.

And what you give up:

• Toughness. This is the trade nobody mentions. Adding fibre makes the part stiffer and more brittle. CF nylon cracks where plain nylon would bend. If your part is there to absorb impact, the fibre is working against you.
• The fibres are abrasive. They chew through a standard brass nozzle in a few hundred grams. Printing them needs a hardened nozzle, which is why the process costs more.
• Cost. The filament is a multiple of PETG, and print speeds are lower.

CF-filled PETG and CF-filled PLA exist too and are a real middle ground: much of the stiffness and stability benefit, much less of the difficulty and cost. Often the right answer when someone asks for carbon fibre.

The thing to be honest about

"Carbon fibre" sounds like it means aerospace-grade strength. It does not. Chopped-fibre filament is not the same material as a layup of woven carbon in resin — not remotely. Those parts get their strength from continuous fibres running the length of the load path. Filament fibres are a fraction of a millimetre long and randomly oriented.

What chopped fibre gives you is stiffness and dimensional stability, not tensile strength. A CF-nylon part is not stronger than a plain nylon part in tension; it is stiffer and more brittle. If somebody is selling you CF filament on strength, they are selling you the wrong story.

And the layer welds are still the weak plane, exactly as in any FDM part — see print orientation and strength.

When to actually reach for it

Use nylon when: the part rubs, cycles, impacts or lives in oil. Gears, bushes, snap latches, wear parts.

Use CF-filled when: the part must be stiff and hold its shape, is large and flat, or needs to survive heat while staying rigid. Jigs, fixtures, drone frames, machine brackets, tooling — see jigs and fixtures.

Use PETG when: you are not sure. Genuinely. PETG handles most functional parts at a fraction of the cost and a fraction of the difficulty, and the honest answer is that most parts asking for nylon do not need it. Start at PLA vs PETG vs ABS.

Where these are the wrong process

• A cheaper material does the job. The most common mistake. Do not pay the nylon tax for a bracket.
• Impact resistance matters and you chose CF. You made the part worse. Plain nylon or PETG.
• Precision requirements. Nylon keeps moving with humidity. It is not the material for a dimension that must hold.
• Safety-critical structure. Still plastic, still layered, still anisotropic. Metal.
• Replacing a real composite layup. Chopped fibre is not that material and cannot be made into it.

Describe what the part does and what has already failed. If PETG will do, we will tell you PETG. Get an estimate · see the materials we print · how pricing works