TPU (thermoplastic polyurethane) prints rubber-like parts — gaskets, phone cases, grips, watch straps, vibration dampers. It also chews up under-tensioned extruders, strings like overcooked spaghetti, and refuses to feed through long Bowden tubes. Get the printer geometry, shore hardness, and speed right and TPU prints reliably; ignore any one of those and you'll fight it forever.
Direct-drive printer only (or a very short Bowden <200 mm). 95A shore hardness for first-timers (softer TPUs are harder to feed). Nozzle 215–230 °C, bed 40–60 °C, print speed 20–30 mm/s, retraction 0.6 mm at 20 mm/s. Dry the filament — TPU absorbs moisture in days. Bambu, Prusa MK4, and Voron toolheads handle TPU fine; long-Bowden Ender 3 stock setups struggle.
"Shore hardness" measures rubber stiffness. The number (with A suffix) ranges from soft (60A, gummy bear) to hard (95A, car tire). Higher numbers print easier; lower numbers are more flexible.
First-time TPU? Use 95A. Successful 95A prints? Try 85A. Don't start at 70A.
TPU strings differently from PLA — the strings are elastic and stretch across the print rather than cleanly snapping. Fixes: