How to Fix TPU Stringing

Flexible filament breaks the usual stringing playbook. The instinct — more retraction, faster retraction — is exactly what jams TPU into the extruder gears. Some stringing is part of the deal with flexibles; here is how to minimize it without turning strings into a jammed printer.

Why retraction can’t save you

Retraction works by yanking the filament back to relieve melt pressure. Rigid filament transmits that pull instantly; TPU stretches like a bungee cord and absorbs it. Long or fast retractions don’t relieve pressure — they stretch the filament, and when it recoils it can buckle sideways and wedge itself in the extruder. That is why Bambu’s TPU profile uses a tiny 0.8 mm retraction at a deliberately slow 10 mm/s — and why you should leave both alone.

The levers that do work

1. Dry it — TPU is thirstier than it looks. Wet TPU strings, bubbles and welds wisps onto every wall. Dry 8 h at 70 °C (and no hotter — TPU can’t take more) whenever the spool has been out of a sealed box for more than a few days. This one step removes more TPU stringing than every slicer setting combined.

2. Come down in temperature. The stock profile prints at 230 °C inside an allowed 200–250 °C window. Cooler TPU is dramatically less oozy: drop 5 °C at a time toward 210–220 °C, watching that extrusion stays consistent — too cold and the soft filament starts skipping in the gears instead.

Bambu Studio / OrcaSlicer: Filament settings → Filament → Nozzle temperature

3. Print slow and steady. Bambu caps TPU at 12 mm³/s of melt flow, and many vendor profiles for bedslingers cap flexibles far lower (RatRig’s TPU baseline allows 5 mm³/s, Creality’s just 2 mm³/s). Respect the cap: pushing flexible filament fast builds melt pressure that has to leak out somewhere, and it leaks out as strings and blobs.

Design and slicing tricks that beat settings

Set the right expectation

A tuned, dry TPU print still carries the odd hair between distant features — flexibles ooze; it is in their nature. The wisps are soft and remove easily with a short blast of hot air. If your parts need crisp, string-free towers, that is a job for a rigid filament, not for more tuning. For the rest of the flexible-printing picture — feed path, plate choice, speed — see the full TPU printing guide; for cross-material theory, the general stringing guide.

Frequently asked questions

Why doesn’t more retraction fix TPU stringing?

Because TPU stretches like a bungee cord and absorbs the pull instead of transmitting it — long or fast retractions don’t relieve melt pressure, they stretch the filament, and when it recoils it can buckle sideways and wedge itself in the extruder. That is why Bambu’s TPU profile uses a tiny 0.8 mm retraction at a deliberately slow 10 mm/s, and why you should leave both values alone.

What settings actually reduce TPU stringing?

Dry the spool first — 8 h at 70 °C, and no hotter — whenever it has been out of a sealed box more than a few days; this one step removes more TPU stringing than every slicer setting combined. Then lower the nozzle temperature 5 °C at a time from the stock 230 °C toward 210–220 °C, and respect the volumetric cap (Bambu allows 12 mm³/s; RatRig 5, Creality just 2).

Can TPU stringing be eliminated completely?

No — a tuned, dry TPU print still carries the odd hair between distant features, because flexibles ooze by nature. The wisps are soft and remove easily with a short blast of hot air. Reduce them by cutting travel moves (print one object at a time), enabling wipe and avoid-crossing options, and if parts truly need crisp, string-free towers, use a rigid filament instead.

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