Carbon or glass fibre filaments: they wear the nozzle, clog or snap

Symptom

With PLA-CF, PETG-CF, PA-CF or other fibre-filled filaments (also glow-in-the-dark or wood ones), less and less material comes out as the nozzle wears, the nozzle clogs often or the filament snaps along the path.

Likely causes, from most to least likely

1. A brass or stainless steel nozzle: fibres are very abrasive and wear it; a hardened steel nozzle is needed.
2. Nozzle or layer too small: Prusa suggests at least a 0.4 mm nozzle and 0.2 mm layers; Bambu Lab recommends 0.6 mm for fibres, and Elegoo does not support a 0.2 mm nozzle with PLA-CF.
3. A badly set first layer: Prusa warns that if it is not right, the risk of clogging the nozzle goes up.
4. Damp filament: fibre-filled nylons are very hygroscopic.
5. Brittle filament snapping at sharp bends in the feed path.
6. Fibre residue building up in the nozzle after long prints.

Checks to tell which one it is

• Check what your nozzle is made of: for abrasive materials, hardened steel.
• If you have already printed fibre with a brass nozzle, suspect wear if under-extrusion keeps getting worse.
• Check the nozzle diameter and layer height in the profile.
• Follow the filament path and look for sharp bends where it could snap.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Fit a hardened steel nozzle

   Switch to a hardened steel nozzle, which Bambu Lab specifies for PA-CF, PLA-CF, PETG-CF, glow-in-the-dark, wood and other hard-particle filaments. If your printer supports it, use 0.6 mm for fibres.

   Check: Extrusion stays steady spool after spool.

   If that does not fix it: Clean the nozzle before printing (next step).

2. Clean nozzle and correct first layer

   Do a cold pull before printing to leave the nozzle clean, as Prusa advises. Set the first layer properly: Prusa warns that a badly set first layer can clog the nozzle. Use a 0.4 mm or larger nozzle and 0.2 mm or thicker layers.

   Check: The first layer comes out flat and continuous.

   If that does not fix it: Dry the filament and check the path (next step).

3. Dry the filament and feed without sharp bends

   Dry the filament as its maker specifies and store it sealed with desiccant. Avoid sharp bends in the feed path: Bambu Lab warns that rigid fibre-filled filaments snap inside the tube.

   Check: No breaks and no moisture stringing.

   If that does not fix it: If it still clogs, go to the next step.

4. If it clogs with use

   Fibres build up in the nozzle with use: clear it with a cold pull or replace it. When switching afterwards to a low-temperature filament such as PLA, first heat to the previous material's temperature and purge until the new one comes out (Bambu Lab).

   Check: The new filament comes out clean.

   If that does not fix it: Replace the nozzle.

5. Protect yourself when handling it

   Bambu Lab warns these filaments can have microscopic barbs on the surface and cut ends: wear cut-resistant gloves and safety glasses when handling them, removing supports or sanding parts. Print in a ventilated place.

   Check: You work without pricks or cuts.

   If that does not fix it: Stop and protect yourself before continuing.

Prevention

• Always use a hardened steel nozzle with fibre filaments.
• Keep the filament dry and the feed path free of sharp bends.
• Replace the nozzle as soon as you notice under-extrusion getting worse.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Composite materials (filled with carbon, kevlar or glass) · Prusa Research
• Introduction to Bambu Nozzles · Bambu Lab
• PET-CF / PPA-CF / PPS-CF / PA6 CF Carbon Fibers Filament Usage Guide · Bambu Lab
• ASA CF / PAHT CF Usage Guide · Bambu Lab
• Guide to FDM Printing Filament (PLA-CF) · Elegoo