Key takeaways
- Fibre buys stiffness and a heat ceiling: Polymaker's published HDT jumps from 111 °C unfilled to 215 °C at 20 % carbon fibre.
- What it costs is ductility — elongation. Nobody publishes it for this family, so do not trust a figure you cannot trace.
- A hardened nozzle is not optional. Chopped fibre wears brass out in tens of hours.
- Drying discipline decides the result more than any slicer setting.
- For hinges, clips and snap fits, unfilled PA12 outperforms PA-CF.
Carbon fibre filament has a marketing problem: the words suggest aerospace, and the product is chopped fibre a fraction of a millimetre long suspended in a thermoplastic. That is genuinely useful, but not in the way the name implies. Here is what it changes.
What the fibre actually does
Short fibres act as reinforcement inside each extruded bead. They raise stiffness sharply, reduce shrinkage as the part cools, and give the surface a matte finish that hides layer lines. They do not bridge the boundary between layers, so interlayer strength does not improve — and in the loading direction across layers, it can drop.
| PolyMide CoPA | Fiberon PA6-CF20 | Fiberon PA6-GF25 | |
|---|---|---|---|
| Tensile strength (ISO 527) | 78.0 MPa | 109.3 MPa | 80.1 MPa |
| Impact, notched Charpy (ISO 179) | 6.9 kJ/m² | 11.0 kJ/m² | 10.0 kJ/m² |
| HDT 0.45 MPa | 111 °C | 215 °C | 191 °C |
| Vicat softening | 180 °C | 219 °C | 212 °C |
| Elongation at break | not published | not published | not published |
| Nozzle required | Brass ok | Hardened | Hardened 0.6 mm |
Read the HDT row. From 111 °C to 215 °C is something no slicer setting buys you — and it is the only reason strong enough to justify everything else filled nylon puts you through.
When PA-CF is the right answer
- Rigid loaded parts — motor mounts, tool holders, machine fixtures where deflection is the failure mode.
- Parts that must hold dimension — a jig that has to stay accurate through thermal cycles. The low shrinkage figure is the real selling point.
- Sliding and wearing surfaces — nylon is self-lubricating, and fibre reduces the creep that makes bushings go slack.
- Large flat parts that warp in unfilled nylon.
When it is the wrong answer
- Living hinges and snap fits. They need elongation. PA-CF will crack on the second cycle where PA12 lasts thousands.
- Impact-loaded parts. A dropped PA-CF bracket can shatter where PA12 dents and continues working.
- Anything cosmetic that has to be a specific colour. The fibre is the colour. It is matte black, and that is the range.
- Printers with brass nozzles and no enclosure. The material will win.
The hardware you need first
- 01
A hardened nozzle, 0.4 mm minimum
Hardened steel or ruby-tipped. Chopped fibre abrades brass in tens of printing hours: the bore goes oval, flow control disappears, and the symptoms look like a slicer problem. A 0.6 mm nozzle also reduces the chance of a fibre bundle jamming the bore.
- 02
An active dry box, not just a dry spool
Polyamide takes on several percent of its weight in water from ordinary room air within hours. Dry at 70 °C for 8–12 hours, then feed the printer from a box held at 50–60 °C for the whole print. On a 12-hour job this is the difference between the first and last layers having the same properties.
- 03
A chamber at 50 °C
Nylon shrinks as it cools, and fibre only partly offsets it. Chamber heat keeps the part from curling off the plate on long prints.
- 04
A plate surface nylon will actually stick to
Smooth PEI is unreliable with nylon. Use a textured PEI sheet or a glue stick layer on glass — and expect the part to need a firm release, not a peel.
Settings that work
ZORVA PA-CF Onyx starting point
- Nozzle
- 285 °C hardened, 0.4–0.6 mm
- Bed
- 90 °C, textured PEI
- Chamber
- 50 °C
- Layer height
- 0.16–0.20 mm
- Walls
- 4, extrusion width 0.48 mm
- Cooling
- 0–20 %
- Drying
- 70 °C / 8 h, then print from dry box
Choosing between the three
One question sorts it. Does the part need to bend? If yes, PA12. If no, and it needs to be stiff and stable, PA-CF. If it also needs to survive above 150 °C, PA6-GF — and budget for nozzle wear, because glass is harder on hardware than carbon.
Frequently asked
Is carbon fibre nylon stronger than regular nylon?
Stiffer, and far more heat resistant. On Polymaker's published figures for annealed specimens, PA6-CF20 reaches 109.3 MPa tensile and 215 °C HDT against 78.0 MPa and 111 °C for unfilled PolyMide CoPA. The honest part: what you give up is ductility, and Polymaker does not publish elongation for this family — if your part has to bend or snap into place, test that part rather than trust a number. Impact resistance drops by roughly two thirds. It resists bending better and fails more suddenly.
Do I need a hardened nozzle for PA-CF?
Yes. Chopped carbon fibre abrades a brass nozzle within tens of printing hours, widening the bore into an oval shape and destroying flow consistency. Use hardened steel or a ruby tip, 0.4 mm minimum and 0.6 mm preferred.
Why does my PA-CF print look furry and weak?
Almost always moisture. Nylon absorbs water from room air within hours, and it flashes to steam in the nozzle, foaming the extrusion. Dry at 70 °C for 8–12 hours and print from a heated dry box rather than an open spool.
Can I print PA-CF without an enclosure?
Small parts, sometimes. Nylon shrinks enough as it cools that larger parts curl off the plate without chamber heat at around 50 °C. Enclosures also matter for particulate containment with fibre-filled grades.
Is PA-CF suitable for gears?
Yes, and it is one of the best FDM options for them: nylon is self-lubricating and the fibre reduces creep, so tooth profiles hold their shape under load. For gears that take impact or shock loading, unfilled PA12 is more forgiving.