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Filament snaps or becomes brittle: causes and what you can do

Troubleshooting7 min readUpdated: 10/2026

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Filament breaks when it has become brittle and is then bent. Manufacturers give three main reasons for this: moisture, tight bends on the way to the extruder, and materials that are brittle by nature, such as some fibre-reinforced filaments. The first step is almost always: dry the filament and store it dry. If it has already broken, you need to get the remaining piece out of the tube, multi-colour system or extruder before you can carry on.

Why PLA in particular becomes brittle after a long time is, incidentally, not conclusively explained. Forums offer several explanations, from moisture through ageing to the stress from the curvature on the spool. Reliable manufacturer information exists mainly for the points below.

Quick test: is the filament brittle?

Unwind a piece of filament and bend it between your fingers. Healthy PLA or PETG bends noticeably before it breaks. If it breaks with only light bending, it is brittle. Mosaic, the maker of the Palette system, names exactly this as the sign to look for: if filament can be snapped without much force, it has probably become too brittle.

The causes

1. Moisture

Bambu Lab writes in its wiki that filament can also break in the print head if it is not dry enough. Typical accompanying signs of damp filament are crackling at the nozzle, more strings and rough surfaces.

What helps: dry it and then store it airtight with desiccant. According to Bambu Lab, freshly dried filament at around 55 % humidity absorbs enough water after only 2 to 12 hours for print quality to suffer. Below 20 % relative humidity it stays dry much longer. Temperatures and times for each material are in Drying and storing filament, boxes, desiccants and target values in Storing filament properly.

2. Tight bends on the way to the extruder

Brittle filament breaks where it is bent most sharply. Bambu Lab names as typical break points the multi-colour system itself, the area in or at the print head, and places where the PTFE tube is sharply bent, for example directly before the extruder.

What helps: route tubes without tight curves. With brittle filament, use paths that are as short and straight as possible, for example the external spool holder instead of the multi-colour system.

3. Material that is brittle by nature

Some filaments are significantly less flexible than PLA or PETG even when new. Bambu Lab lists as “too brittle” for the AMS and AMS lite, among others, certain PET-CF types, wood-filled PLA, and PA-CF/GF and PAHT-CF/GF. With the CFS, Creality warns that hard filaments such as PPA-CF or PPS-CF can break in the tube.

What helps: according to the manufacturer’s list, do not feed such materials through the multi-colour system but directly from the spool. More on these filaments can be found in Fibre-reinforced filaments.

4. Repeated heating and cooling

For PC, Bambu Lab points out that the filament can become brittle after several drying cycles with heating and cooling. According to the manufacturer, the printed parts are not affected by this, but the filament breaks more easily during printing. Bambu Lab therefore advises storing dried PC airtight with desiccant straight away instead of drying it again and again.

5. Unfavourable storage

Manufacturers recommend storing filament cool, dry, out of direct sunlight and away from heat sources. A spool that lies open next to the window for months has several disadvantages at once.

Overview

SignLikely causeFirst step
Breaks when bent, crackles when printingmoisturedry it, store airtight
Always breaks at the same point in the tubetight bendroute the tube differently
Fibre-reinforced material breaks in the AMS or CFSmaterial too brittle for the systemprint directly from the spool
PC becomes brittle after repeated dryingheat cyclesstore airtight after drying, do not keep re-drying

Filament broken in the AMS or in the tube

Bambu Lab printers usually report this as “filament broken in the path”. According to the Bambu Lab wiki, this is how to proceed:

  1. Break at the AMS outlet: Release the PTFE tube at the AMS outlet. To do this, press the lock on the connector down and pull the tube out. Remove the remaining piece, push the tube back in firmly and select “Retry” on the printer.
  2. Break in the tube between the AMS and the printer: Release the tube at both ends and push the remaining piece out with a long, intact piece of filament. For the AMS lite, Bambu Lab describes exactly this approach.
  3. Break inside the AMS or in the hub: For this the unit has to be partly taken apart. The wiki has separate instructions for each model. Switch the printer off and disconnect it from the mains first.

For other systems such as the CFS or ACE, follow the instructions of the respective manufacturer.

Filament broken in the extruder

If the broken piece is stuck in the extruder or the hotend, there are two ways. Prusa describes both in its knowledge base:

  1. Heat the nozzle. In the instructions for the MK3 series, Prusa gives 280 °C and a waiting time of 3 to 5 minutes. For other printers, follow the manufacturer’s instructions.
  2. Open the extruder, that is, release the lever or the tension screw so that the gears let go of the filament.
  3. Pull it out: If 0.5 to 1 cm still sticks out, grip the piece with needle-nose pliers and pull it upwards slowly, bit by bit.
  4. Push it through: If it broke off directly at the tube edge, push it down through the hot nozzle with a thin tool or a piece of filament 1 to 1.5 mm in diameter.

On Bambu Lab printers, according to the wiki, it often helps to release the PTFE tube at the print head and push the filament through or pull it out from behind. After that it is worth taking a look into the extruder: abrasion residue on the gears and the filament sensor should be removed, otherwise there will be problems the next time you load. If something is stuck in the nozzle itself, Clogged nozzle will help.

Caution: the hotend and nozzle are hot while you work. Do not reach near the heater block with bare hands.

Can brittle filament be saved?

If moisture is the cause, usually yes: after drying, the filament bends noticeably better again and breaks less often. If it still breaks after drying, print it with the shortest, straightest path possible directly from the spool. For materials that are too brittle, Bambu Lab expressly recommends the external spool holder instead of the AMS lite. If it stays brittle anyway, the spool is hardly usable for printing any more.

Prevention

  1. Store opened spools airtight with desiccant after printing, target under 20 % humidity.
  2. If in doubt, dry before printing.
  3. Route tubes without tight curves.
  4. Feed brittle speciality filaments only in the way the manufacturer of the multi-colour system approves.
  5. Do not store spools in the sun or next to the radiator.

Continue with: Drying and storing filament, Storing filament properly and Respooling filament, refill spools and joining filament.

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