About this video
Why TPU Prints Fail and How to Fix Them
TPU (thermoplastic polyurethane) is one of the most popular flexible filaments for 3D printing, but it is also one of the trickiest to dial in. If your TPU prints look stringy, blobby, or weak, the problem usually comes down to three settings: flow, moisture, and retraction. This guide walks through each fix so you can 3D print TPU perfectly on almost any FDM printer.
Step 1: Lower the Max Flow Ratio
Open your slicer (Cura, PrusaSlicer, OrcaSlicer, Bambu Studio, etc.) and navigate to the filament settings. Scroll down to Max Flow Ratio (sometimes called Maximum Volumetric Flow or Flow Rate). If the value is set above 3 mm³/s, lower it to around 2–3 mm³/s for TPU. Flexible filament does not melt and flow as quickly as PLA or PETG, so pushing too much material through a hotend causes under-extrusion, blobbing, and poor layer bonding. A slower, controlled flow gives the melt zone time to keep up and produces cleaner walls.
Step 2: Dry Your TPU Filament
TPU is hygroscopic, meaning it absorbs moisture from the air faster than most filaments. Wet TPU pops, hisses, and prints with rough, fuzzy surfaces. To fix this, dry your spool in a filament dryer, food dehydrator, or oven at 55 °C for 8 hours. For long-term storage, keep the spool in a sealed bag with desiccant so it stays dry between prints. Properly dried TPU prints smoother, bonds better between layers, and has noticeably stronger mechanical properties.
Step 3: Turn Off Retraction
Retraction is the biggest source of TPU stringing and jamming. Because the filament is soft and compressible, it often gets chewed up by the extruder gear instead of pulling back cleanly. Go to Settings → Per-Model Settings Overrides (or add a process override) and set Retraction to 0 mm. Without retraction, you may see slight stringing on travel moves, but you will eliminate the grinding, clogging, and inconsistent extrusion that ruin TPU prints. If you still want some retraction, keep it under 1 mm and disable Z-hop.
Quick TPU Printing Tips
- Print slow: 20–30 mm/s is a safe starting speed.
- Use a direct-drive extruder when possible; Bowden setups need extra tuning.
- Set nozzle temperature between 210–230 °C and bed at 40–60 °C.
- Use a textured or PEI sheet for better first-layer adhesion.
FAQ
What is the best speed for TPU?
Start at 20–30 mm/s. Slower speeds reduce pressure buildup in the hotend and improve print quality.
Can I print TPU without a direct-drive extruder?
Yes, but you will need very low retraction (0.5 mm or less) and slower speeds to avoid grinding.
How do I know if my TPU is wet?
Look for popping or hissing sounds at the nozzle, steam, and rough, bubbly surfaces. Drying at 55 °C for 8 hours restores print quality.
Should I turn off retraction for all flexible filaments?
Yes, disabling retraction is a reliable fix for TPU, TPE, and other soft filaments and prevents extruder grinding.
