Key takeaways
- TPU jams because the strand buckles in the extruder, not because it is soft.
- Retraction is the first thing to reduce and the last thing to increase.
- 95A prints almost anywhere. 85A needs direct drive and patience.
- A gasket seals through geometry and compression, not through material softness.
Flexible filament has a reputation for being difficult, and the reason is mechanical rather than chemical. TPU is a spring. Push a spring down a tube with a gap in it and it bows sideways instead of moving forward. Nearly every TPU problem is a version of that.
Pick the hardness by how much the part must deform
| TPU 95A | TPU 85A | |
|---|---|---|
| Feel | Firm, like a skateboard wheel | Soft, like a rubber band |
| Elongation at break | 551 % | 592 % (at 90A) |
| Tensile strength | not published | 30.1 MPa (at 90A) |
| Print speed | 15–35 mm/s | 10–20 mm/s |
| Extruder | Direct drive preferred | Direct drive required |
| Typical use | Grips, feet, seals, strain relief | Soft-touch pads, damping mounts, liners |
Most people who ask for the softest option want 95A. It bends convincingly, seals well, and prints without a fight. Choose 85A only when the part has to squash — vibration damping, wearable padding, a bulb you press.
Get the filament path right before touching the slicer
- Direct drive wins because the unsupported length between gear and melt zone is millimetres instead of half a metre.
- Close every gap. Any space between the drive gear and the hot end inlet is where the strand will buckle. Guide tubes should butt up hard against both.
- Loosen the idler tension. Over-tight gears bite into TPU, deform it, and change its effective diameter. Set it just tight enough not to slip.
- Feed from a smooth spool. Flexible filament grips its own coils. If the spool has rough flanges, unwind and re-spool it.
Settings that work
ZORVA TPU 95A Graphite starting point
- Nozzle
- 225 °C, 0.4 mm (0.6 mm for seals)
- Bed
- 50 °C, textured PEI, no adhesive needed
- Speed
- 20 mm/s outer wall, 25 mm/s infill
- Retraction
- 0.6 mm at 20 mm/s
- Acceleration
- 500–800 mm/s², jerk low
- Cooling
- 50 %
- Layer height
- 0.2 mm
- Drying
- 60 °C / 6 h before first use
Two of those matter more than the rest. Low acceleration stops the elastic strand from lagging behind the commanded move, which is what produces uneven extrusion on curves. Low retraction stops the extruder pulling a stretched section of filament back into the cold zone, where it stays stretched and then under-extrudes.
If you have stringing and you are about to increase retraction: dry the spool first. Wet TPU strings more than badly tuned TPU.
Designing a printed TPU part that works
- 01
For seals, print solid with concentric top and bottom
Infill patterns leave internal channels that leak. Set 100 % infill with concentric top and bottom surfaces so the extrusion paths follow the sealing face rather than crossing it.
- 02
Use a wider nozzle than you think you need
A 0.6 mm nozzle makes each bead wider than the gap a leak would follow, and reduces the number of bead boundaries through the wall. It is the single biggest improvement to a printed gasket.
- 03
Design in 15–20 % compression
A printed gasket seals when it is squeezed, not when it fits. Size the groove so the part is meaningfully over-compressed at assembly.
- 04
Avoid thin vertical walls in soft grades
In 85A, a 1 mm wall will fold over during printing. Either thicken it or reorient the part so that face is printed flat.
- 05
Expect to sand nothing
TPU does not sand — it smears. Design the surface you want, because you will not be finishing it afterwards.
Troubleshooting, in order
| Symptom | First thing to check | Then |
|---|---|---|
| Grinding, no extrusion | Gap in the filament path | Reduce speed, loosen idler |
| Stringing everywhere | Moisture — dry at 60 °C / 6 h | Lower nozzle 5–10 °C |
| Under-extrusion on curves | Acceleration too high | Reduce retraction distance |
| Part sticks to plate too well | Bed too hot | Drop to 40 °C, textured sheet |
| Seal leaks | Infill pattern, not material | Solid, concentric, 0.6 mm nozzle |
Both ZORVA flexible grades ship with these settings on the Material Passport, including the drying schedule, which is the step most people skip.
Frequently asked
Can I print TPU on a Bowden extruder?
TPU 95A yes, with speeds under 20 mm/s, retraction at 0.8 mm or less, and a tight filament path with no gaps. Softer 85A buckles inside the tube and is not practical on Bowden systems.
What is the difference between 95A and 85A TPU?
Shore hardness. 95A is firm — think skateboard wheel — and prints at 15–35 mm/s on most direct-drive printers. 85A is genuinely soft and rubbery, stretches further, and needs 10–20 mm/s and a direct-drive extruder with a fully constrained filament path.
Why is my TPU print stringing so much?
Moisture first, temperature second, retraction third. TPU absorbs water quickly; dry at 60 °C for six hours before adjusting anything. Then lower the nozzle 5–10 °C. Increase retraction last, because too much retraction causes under-extrusion in flexible filament.
How do I make a 3D printed gasket seal?
Print it solid with concentric top and bottom layers so no extrusion path crosses the sealing face, use a 0.6 mm nozzle so each bead is wider than any leak path, and design the groove so the gasket is compressed 15–20 % at assembly.
What temperature does TPU need?
Around 220–235 °C for 95A and 215–230 °C for 85A, with a bed at 40–60 °C. Higher temperatures improve layer bonding but increase stringing, so tune from the middle of the range after drying the filament.