TPU & flexible filaments — the complete guide
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 — pick the right TPU first
"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.
| Shore | Feel | Printer compatibility | Use for |
|---|---|---|---|
| 95A | Like a roller-blade wheel | Almost any printer, including Bowden | Phone cases, watch straps, grips, gaskets |
| 90A | Stiff rubber | Most direct drive; some Bowden | RC tires, durable gaskets |
| 85A | Pencil eraser | Direct drive only | Soft gaskets, vibration dampers |
| 80A | Soft pencil eraser | Quality direct drive only | Stretchy bands, soft toys |
| 70A–60A | Gummy candy | Specialist setups (Bambu, Voron, MK4) | Stretchy fabric, foam-like parts |
First-time TPU? Use 95A. Successful 95A prints? Try 85A. Don't start at 70A.
Printer requirements
- Direct-drive extruder — the filament path between the gear and the melt zone must be short and constrained. Bowden tubes longer than ~200 mm cause the filament to compress like a spring and you lose extrusion control.
- Constrained filament path — the filament should have nowhere to buckle. Some extruders have a built-in PTFE guide tube; others don't and you'll need to add one.
- Geared dual-drive extruder (BMG, Sherpa Mini, Bambu/Prusa stock) feeds TPU much better than a stock single-gear extruder.
- Idler tension should be moderate. Too tight and you crush soft TPU; too loose and it slips.
Recommended print settings
| Setting | Range | Notes |
|---|---|---|
| Nozzle temperature | 215–230 °C (95A); 220–240 °C (softer) | Higher temp = better layer bonding but more oozing. |
| Bed temperature | 40–60 °C | Higher than 60 makes removal nearly impossible. |
| Print speed | 20–30 mm/s | Slow! TPU compresses under speed. Bambu can do 80 with their high-flow profiles. |
| Acceleration | 500–1500 mm/s² | Lower than rigid filaments — sudden direction changes cause compression bumps. |
| Part cooling | 30–100% | Less affects layer bond on TPU; 50% is safe default. |
| Retraction distance | 0.4–1.2 mm | Less than you'd use for PLA; over-retraction pulls TPU out of the melt zone irrecoverably. |
| Retraction speed | 15–25 mm/s | Slow retract; soft TPU compresses if jerked. |
| Layer height | 0.16–0.28 mm | Thicker layers print faster and bond better on TPU. |
| First-layer flow | 105–115% | Slight over-extrusion helps the soft material grip the bed. |
| Bed surface | Smooth or textured PEI works fine, no glue | TPU sticks to PEI cleanly and releases without damage. |
| Drying | 55 °C for 8–12 hours | TPU absorbs moisture in days. Dry it. |
Stringing on TPU
TPU strings differently from PLA — the strings are elastic and stretch across the print rather than cleanly snapping. Fixes:
- Dry the filament. Wet TPU is the #1 stringing cause — far more important than retraction tuning.
- Lower temperature 5 °C at a time until under-extrusion appears, then back up 5.
- Enable combing — reroutes travel moves to stay inside the part.
- Disable Z-hop — Z-hop pulls TPU strings to the new location.
- Reduce retraction speed to 15 mm/s — soft TPU compresses, not retracts, if pulled too fast.
Strengths
- Flexible: elongation at break up to 500%.
- Abrasion-resistant: better wear life than PLA or PETG by orders of magnitude.
- Vibration damping: excellent for shock-absorbing parts.
- Chemical resistance: resistant to oils and most chemicals.
- UV stable: better than PLA; comparable to PETG.
- Holds detail at large feature sizes: not great for miniatures, fine for everyday shapes.
- Recyclable: thermoplastic; can be remelted into new pellets.
Weaknesses
- Bowden = pain. Long Bowden tubes effectively rule out TPU softer than 95A.
- Slow: 20–30 mm/s makes large parts take a long time.
- Strings badly: tuning helps but doesn't fully solve it.
- Hygroscopic: dry storage mandatory.
- Limited resolution: can't hold tiny features; not for jewelry or miniatures.
- Pricey: $35–$60/kg vs $20 PLA.
- Bonds poorly: most CA / epoxy doesn't stick. Use TPU-specific glue or a flame torch (lightly).
When to choose TPU
- Phone cases and protective covers.
- Watch straps and wearables.
- Gaskets, seals, O-ring replacements.
- Tool grips and handle covers.
- RC tires and shock-absorbing parts.
- Vibration-damping feet for machines.
- Flexible hinges (with PETG: print PETG body, TPU hinge).
- Toys and squeezable objects.
Related articles
Sources & further reading
- Prusa Knowledge Base — Flexible filaments
- Bambu Lab Wiki — TPU printing guide
- NinjaTek — NinjaFlex datasheets