Filament snaps inside the tube on its own
Brittle filament is almost always old, poorly stored or cheap filament. In many cases, drying it recovers it; in others, you have to accept that it has degraded.
What the failure looks like
When loading filament, it snaps with a sharp crack, or the print stops and you find a loose piece inside the tube.
Causes, most likely first
- 01
Moisture and ageing
PLA is a polyester that hydrolyses: over time and with moisture, it loses molecular chain length and becomes brittle.
- 02
Bend radius too tight
A bowden tube with a very tight curve will break already weakened filament.
- 03
Filament trapped on the spool
A loop trapped under another creates tension and snaps it.
- 04
Very low ambient temperature
In winter and in garages, PLA becomes more brittle.
Step-by-step fix
1. Dry the spool
PLA at 45-50 °C for 4-6 h. Do not exceed 55 °C or the spool will stick together.
2. Check the filament path
Smooth out the tube bends, avoid sharp angles, and check that the spool rotates freely.
3. Discard the damaged section
The first few metres of an old spool are usually the worst.
4. If it keeps breaking, retire it
A three-year-old poorly stored PLA will not fully recover. Use it for calibration tests.
So it doesn't happen again
- Airtight bag with silica gel for anything you are not using.
- Label spools with the date they were opened.
- Buy quantities you will use within months, not years.
Related questions
Can it be dried in a domestic oven?
Yes, with the oven at its lowest setting (usually 50 °C) and monitoring with a separate thermometer: many ovens overshoot by 20 °C and warp the spool.
Keep reading
What if it isn't worth your time?
Sometimes the part is more urgent than the learning curve. We're a workshop in Viladecavalls: send us the file and we'll print it with the right material and settings.
Still not working?
Tell Marco which printer and material you use and he'll tell you what to change.
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