PLA turns brittle and snaps on the spool, in the tube or in the multi-colour system

Symptom

The PLA filament breaks when you bend it by hand, snaps inside the PTFE tube, the multi-colour system or the extruder and the print stops for lack of filament, or the printer reports a broken filament in the path.

Likely causes, from most to least likely

1. Moisture: Elegoo explains that damp filament becomes more brittle, and Bambu Lab that it can break inside the toolhead if it is not dry enough. Prusa points out that PLA changes less with moisture than other materials, such as nylon.
2. Sharp bends in the path: Bambu Lab notes that brittle filament breaks mostly where the PTFE tube bends sharply just before the extruder.
3. Pulling during loading and unloading in a multi-colour system: Bambu Lab warns that brittle filament can break while being fed or pulled back in the AMS.
4. PLA is stiff and inflexible by nature (Prusa describes it as brittle), so it copes badly with bending.
5. Filaments more fragile than regular PLA, such as glow-in-the-dark or third-party fibre-filled ones: Bambu Lab advises against putting overly hard or brittle filaments in the AMS lite.

Checks to tell which one it is

• Bend a piece of the filament end: if it snaps instead of bending, it is brittle.
• Look at where it broke: inside the multi-colour system, between it and the printer, at the tube bend before the extruder or inside the toolhead.
• Think about how long the spool has been out and how it was stored; a hygrometer in the box tells you the real humidity.
• Follow the tube's route and look for sharp bends or squashed sections.

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. Remove the broken piece with the printer off

   Switch off and unplug the printer before taking anything off the toolhead. If the piece is at the bend before the extruder, Bambu Lab suggests releasing the PTFE tube and pushing or pulling the filament from the back; if it is in the multi-colour system, release the tube from its outlet and take the piece out, or push it out with another filament.

   Check: The path is clear and new filament reaches the extruder.

   If that does not fix it: If the piece is inside the extruder, follow your printer's extruder cleaning guide.

2. Dry the PLA

   Dry the spool before carrying on: Elegoo recommends 55 ± 5 °C for 6 h for PLA, and Prusa uses 45 °C for 6 h for its own; do not exceed the maker's temperature or the turns will soften and stick together. Do not use a microwave or kitchen oven: Bambu Lab advises against it and Prusa warns that home ovens measure temperature poorly.

   Check: The filament bends again without snapping.

   If that does not fix it: If it still snaps cleanly, check the path (next step).

3. Remove sharp bends from the path

   Place the spool and the tube so the filament reaches the extruder with no sharp bends or squashed sections. If the tube bends very sharply just before the extruder, check how it should be routed in your printer's manual.

   Check: The filament moves without rubbing or bending anywhere.

   If that does not fix it: If it always breaks in the same place, print that spool outside the multi-colour system (next step).

4. Print from outside the multi-colour system

   If the spool is still fragile or is a filament your maker does not support in the multi-colour system (Bambu Lab advises against very hard or brittle ones in the AMS lite), print it from the external spool holder, with the shortest possible path.

   Check: The print finishes without breaks.

   If that does not fix it: If it still breaks, try another spool of the same type to rule out a faulty one.

5. Store it dry so it does not happen again

   Keep PLA in its bag with desiccant or in an airtight box and, if you can, print from a dry box. Bambu Lab explains that most filaments only stay dry below 20% relative humidity and that, at 55% at home, a freshly dried one picks up moisture again within 2-12 hours.

   Check: The spool stays flexible from one print to the next.

   If that does not fix it: Replace or regenerate the desiccant if it is no longer effective.

Prevention

• Seal the bag or box with desiccant as soon as you finish printing.
• Avoid sharp bends in the tube, especially just before the extruder.
• If a PLA turns brittle, dry it before looking for other causes.

Still not fixed?

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Printers it applies to

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

Material: PLA.

Official sources

This guide summarises the official documentation linked here:

• Filament break in the path · Bambu Lab
• AMS lite FAQ (hard or brittle materials) · Bambu Lab
• Filament Drying Recommendations · Bambu Lab
• Guide to FDM Printing Filament (drying and brittleness) · Elegoo
• Drying filament · Prusa Research
• PLA (material guide) · Prusa Research