Glossary
TPU
TPU is a flexible, rubber-like filament used for phone cases, gaskets and grips, printed slowly and best on a direct drive extruder.
TPU, or thermoplastic polyurethane, is a flexible filament that behaves more like soft rubber than rigid plastic once printed. It comes in a range of hardness levels, and the softer versions can stretch and bend repeatedly without cracking, which is why it shows up in phone cases, cable grips, gaskets, wheels and other parts that need some give.
Because TPU is soft, it can buckle or jam inside a long, flexible feed path instead of pushing cleanly into the hotend. A direct drive extruder, which sits right above the hotend, generally handles TPU far more reliably than a bowden setup where filament travels through a long tube before reaching the nozzle.
Successful TPU prints usually mean printing slower than PLA or PETG, reducing or disabling retraction distance, and keeping the print cooling fan on to help each flexible layer hold its shape as it cools. A common mistake is trying to print TPU fast on a bowden printer, which usually ends in grinding, skipped steps or a filament jam rather than a finished part.