Very soft TPU (85A or softer): only with a direct drive extruder, a short path and very slowly

Symptom

With a very soft TPU (for example 82A or 85A), the filament buckles or gets squashed between the extruder gears, winds up inside the toolhead, does not feed through the tube, or the part comes out with gaps because it jams now and then.

Likely causes, from most to least likely

1. A hardness below what your printer supports: Bambu Lab does not support TPU softer than 85A, and Creality requires 95A or harder on the K1C and K1 Max and does not support 90A or softer on the K2 Plus. The softer it is, the harder it is to print (Prusa).
2. A long path or one with friction: soft TPU buckles inside PTFE tubes and multi-colour systems. Creality advises against feeding it through the PTFE tube on the K2 Plus, and Elegoo asks for a direct drive extruder for TPU.
3. Gears pressing too hard: Creality explains that a TPU that is too soft can be flattened by the extruder gear and clog the nozzle; Prusa asks you to loosen the pressure so it pushes gently.
4. Too much speed: Creality stays at or below 2 mm³/s of volumetric flow with generic TPU on the K2 Plus, and Prusa prints flexibles at about 20 mm/s.
5. A nozzle that is too small or has residue: Bambu Lab does not support its TPU 85A with a 0.4 mm nozzle and asks for a new nozzle or cold pulls before TPU.
6. Retraction and automatic calibrations designed for rigid filaments: Creality and Bambu Lab ask you to turn off flow calibrations before printing TPU.

Checks to tell which one it is

• Check the Shore hardness on the label (82A, 85A, 95A…) and compare it with the minimum your printer supports.
• Check whether your extruder is direct drive (mounted on the toolhead) or Bowden (with a long tube to the toolhead).
• Follow the filament path from the spool: tubes, sensors and multi-colour systems in the way.
• If the filament comes out squashed or wound around the gears, they press too hard or you are going 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. Check whether your printer supports it

   Before loading it, check your maker's minimum hardness: Bambu Lab, 85A (and for its TPU 85A, a 0.6 mm nozzle or larger); Creality, 95A on the K1C and K1 Max and harder than 90A on the K2 Plus. If your TPU is softer than your printer supports, do not force it: use a harder one, such as a 95A.

   Check: Your spool's hardness is within what the printer supports.

   If that does not fix it: If it is not supported, switch to a harder TPU before going on.

2. Feed it directly by the shortest path

   Take the TPU out of the multi-colour system and feed it from a separate spool placed higher than the printer. On some printers you need to remove the lid and feed it from the top straight into the extruder, without the PTFE tube: Bambu Lab asks for this for its TPU 85A on the P series, and Creality on the K1C, K1 Max and K2 Plus.

   Check: The filament enters the extruder without buckling or dragging.

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

3. Loosen the extruder and load slowly

   Loosen the gear pressure so they push gently (Prusa). When loading, heat the nozzle (Bambu Lab uses 250 °C) and press extrude a little at a time, not repeatedly, so the TPU does not wind around the gears. On the CORE One+ and CORE One L, Prusa includes a switch that loosens the filament sensor lever for loading flexibles.

   Check: The filament comes out of the nozzle continuously.

   If that does not fix it: Slow down (next step).

4. Print very slowly

   Keep the TPU profile's volumetric speed and do not raise it (Bambu Lab). As a reference, Prusa prints flexibles at about 20 mm/s and at most 30-40 mm/s, and Creality asks for under 50 mm/s on the K1C and K1 Max when slicing with third-party software.

   Check: It no longer winds up or jams.

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

5. Minimal retraction and calibrations off

   Reduce retraction or turn it off and raise it gradually (Prusa). Turn off automatic flow and pressure advance calibration before printing TPU (Bambu Lab, Creality). If you feel a lot of resistance, raise the nozzle by 5 °C (Prusa).

   Check: The part comes out without gaps or jams.

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

6. A clean, suitable nozzle

   Before TPU, do several cold pulls with PLA or PETG or fit a new nozzle; if you printed carbon or glass fibre before, do more of them (Bambu Lab). With TPU 85A, Bambu Lab asks for a 0.6 or 0.8 mm nozzle.

   Check: The TPU flows continuously from the start.

   If that does not fix it: If it still jams, switch to a harder TPU.

Prevention

• Before buying a very soft TPU, check the minimum hardness your printer supports.
• Always print TPU from a separate spool, with a short path and no multi-colour system.
• Keep it dry: TPU absorbs moisture very easily.

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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:

• TPU Printing Guide · Bambu Lab
• TPU 85A&90A printing guide for P series · Bambu Lab
• How to use K2 Plus to print TPU filament · Creality
• How to Print TPU for K1C & K1Max · Creality
• Flexible materials (material guide) · Prusa Research
• Guide to FDM Printing Filament (TPU) · Elegoo