TPU and flexibles: they tangle in the extruder, jam in the tube or the multi-colour system, or string

Symptom

With TPU or another flexible filament, the filament buckles and tangles in the extruder gears, does not feed through the PTFE tube (especially on Bowden printers or long paths), the part has gaps because it jams, or there are lots of strings and blobs.

Likely causes, from most to least likely

1. Filament too soft for your printer: the softer, the harder to print. Creality requires 95A or harder on the K1C and K1 Max and does not support 90A or softer on the K2 Plus; Bambu Lab does not support below 85A.
2. Too much resistance along the path: long PTFE tubes, Bowden printers or going through a multi-material system. Creality does not allow TPU in the CFS and Bambu Lab only supports its «TPU for AMS» in the AMS.
3. Too much speed: Prusa suggests about 20 mm/s and at most 30-40 mm/s.
4. The extruder gear presses too hard and crushes or tangles the filament.
5. Too much retraction, or automatic flow calibrations meant for rigid filaments that Creality and Bambu Lab ask you to turn off for TPU.
6. Damp filament, or residue of high-temperature or fibre-filled materials in the nozzle.

Checks to tell which one it is

• Check the Shore hardness on the label (for example 95A) and compare it with what your printer supports.
• Follow the filament path: long or curved tubes, sensors or multi-colour systems in the way.
• Check the profile's speed and retraction.
• If the filament comes out crushed or wound around the gears, the extruder presses too hard or runs too fast.

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. Feed directly, not through the multi-colour system

   Take the TPU out of the multi-colour system and feed it from a separate spool, with the path as short and straight as possible. On the K1C, K1 Max and K2 Plus, Creality suggests unplugging the PTFE tube from the extruder, securing it aside and feeding the filament from the top, with the spool higher than the printer.

   Check: The filament goes in without buckling or snagging.

   If that does not fix it: Loosen the extruder and slow down (next step).

2. Loosen the extruder and slow down

   Loosen the gear pressure so it pushes gently (Prusa suggests loosening the idler screws by 1.5 turns if it tangles). Print slowly: about 20 mm/s. Creality asks for under 50 mm/s on the K1C and K1 Max with third-party slicers and, on the K2 Plus, no more than 2 mm³/s volumetric flow with generic TPU.

   Check: The filament no longer winds around the gears.

   If that does not fix it: Adjust temperature, retraction and calibrations (next step).

3. Temperature, retraction and calibrations

   Use the maker's temperature (Prusa: 220-240 °C for its TPU 95A; 230-245 °C for flexibles in general, and 5 °C more lowers resistance; if the surface is poor or it oozes, Creality and Bambu Lab suggest lowering it). Reduce retraction or turn it off and raise it gradually. Turn off automatic flow and pressure advance calibration before printing TPU.

   Check: It prints without jams and with fewer strings.

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

4. Clean the nozzle before TPU

   Before TPU, clear out residue of high-temperature materials (Creality mentions those printed above 240 °C) or fibre-filled ones: Bambu Lab recommends a new nozzle or several cold pulls.

   Check: TPU flows continuously from the start.

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

5. Dry and store the TPU

   Dry TPU before printing (Prusa: at least 4 h at 60 °C for its TPU 95A; Creality uses 70 °C for 8 h) and keep it in a dry box; Bambu Lab advises below 20% relative humidity.

   Check: Bubbles and strings disappear.

   If that does not fix it: If the printer does not support that hardness, switch to a harder TPU.

6. Right build plate

   On smooth PEI apply glue as a release layer: TPU grips so hard it can damage it. The powder-coated textured plate does not need it.

   Check: The part comes off without tearing the surface.

   If that does not fix it: On the textured plate, if it is hard to remove, Prusa suggests heating it to 40 °C and using a spatula.

Prevention

• Choose a TPU hardness your printer supports; 95A is one of the easiest to print.
• Always print TPU from a separate spool with a short path.
• Store TPU in a dry box with desiccant.

Still not fixed?

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Printers it applies to

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

Material: TPU.

Official sources

This guide summarises the official documentation linked here:

• Flexible materials (material guide) · Prusa Research
• Prusament TPU 95A material guide · Prusa Research
• How to use K2 Plus to print TPU filament · Creality
• How to Print TPU for K1C & K1Max · Creality
• TPU Printing Guide · Bambu Lab
• CFS Filament Compatibility Description · Creality