TPU Flexible Filament: A Beginner's Guide
TPU (Thermoplastic Polyurethane) is the material that makes 3D printing genuinely useful for a whole category of things other plastics can't touch - phone cases, gaskets, wheels, grips, wearables, and anything that needs to flex or absorb impact.
It's also one of the trickier filaments to print well. Here's everything you need to know.
What Is TPU?
TPU is a flexible, rubber-like plastic. It ranges from very soft and stretchy (Shore 85A - similar to a rubber band) to relatively firm and only slightly flexible (Shore 98A - similar to a hard rubber sole).
For beginners, 95A hardness is the sweet spot - flexible enough for most applications, firm enough to print reliably.
Popular TPU filaments:
- eSUN TPU 95A - consistent, affordable, widely available
- Polymaker PolyFlex TPU95 - excellent quality, slightly easier to print
- SainSmart TPU - budget option, good results
TPU Print Settings
| Setting | Recommended Value |
|---|---|
| Nozzle temperature | 220-235°C |
| Bed temperature | 30-60°C |
| Print speed | 20-30mm/s |
| Retraction | 0-2mm (direct drive) / Minimal (Bowden) |
| Cooling | Moderate (30-50%) |
| Infill | 20-40% for flexibility, 60%+ for rigidity |
Slow down. TPU does not respond well to speed. 25mm/s is a safe starting point - you can push to 40mm/s once you understand how your printer handles it, but anything faster risks bunching and jams.
Direct Drive vs Bowden: This Actually Matters for TPU
This is the most important thing to know about printing TPU:
Direct drive printers (extruder motor on the toolhead) handle TPU well. The short, direct path from extruder to nozzle gives the flexible filament no room to buckle or bunch.
Bowden printers (motor on the frame, long PTFE tube to hotend) struggle badly with TPU. The flexible filament compresses and buckles in the long tube, causing massive under-extrusion, jams, and inconsistent flow.
If you have a Bowden printer like an older Ender 3 (non-SE/V3), TPU is possible but frustrating. Slow way down (15-20mm/s) and reduce retraction to near zero.
If you have a direct drive printer (Ender 3 V3 SE, Bambu Lab, Prusa MK4, etc.), TPU prints reasonably well with the settings above.
Retraction Settings for TPU
This trips up most beginners.
Too much retraction with flexible filament causes the extruder to grind against the soft material or cause the filament to buckle in the drive path.
Direct drive: Start with 0-2mm retraction at slow speed (20mm/s). Many TPU prints work better with retraction off entirely.
Bowden: Retraction should be 0-1mm maximum, or disabled. Counter-intuitive, but less retraction usually means fewer jams with TPU.
Why TPU Jams (and How to Avoid It)
The most common TPU problem is the filament bunching up between the extruder gear and the hotend entry. This happens because:
- Speed too high - TPU can't keep up and buckles
- Too much retraction - pulls the soft filament back into the extruder mechanism where it jams
- Bowden tube gap - any gap between the PTFE tube and nozzle gives TPU room to bunch
Prevention:
- Slow print speed (25mm/s)
- Minimal or no retraction
- Make sure your PTFE tube seats fully against the nozzle
- Use a Capricorn PTFE tube with its tighter 1.9mm inner diameter
Bed Adhesion for TPU
TPU sticks well to most surfaces - sometimes too well.
- PEI textured sheet - excellent adhesion, but parts can be hard to remove. Let the bed cool fully before removal.
- Glass with glue stick - good adhesion and easier removal
- Blue painter's tape - works well, parts release easily
If parts stick too aggressively to your PEI sheet, try a thin layer of hairspray or glue stick on top of it as a release agent.
Useful Things to Print in TPU
TPU really shines for functional, everyday items:
- Phone cases - custom-fitted, shock-absorbing
- Cable ties and clips - flexible and reusable
- Gaskets and seals - custom shapes for enclosures and projects
- Wheels and tyres for RC cars and robots
- Grips and handles - tool handles, jar openers
- Watch straps - surprisingly good quality
- Shoe insoles - with the right infill settings
- Ear tips for earphones
- Vibration dampeners for printers and electronics
Find TPU designs at Printables.com and Thingiverse.
TPU Storage
TPU is highly hygroscopic - it absorbs moisture quickly and prints worse when wet. Signs of wet TPU: popping sounds, surface bubbles, weaker parts.
Store in an airtight container with silica gel desiccant. Dry at 45-50°C for 4-6 hours in a filament dryer if prints are coming out poorly.
Shore Hardness: What the Numbers Actually Mean
Shore A is the scale used for soft materials like rubbers and flexible plastics. The lower the number, the softer and stretchier the material.
| Shore A | Feel | Typical Uses |
|---|---|---|
| 85A | Very soft, stretchy | Soft gaskets, stress-relief grips |
| 90A | Moderately flexible | Shoe insoles, soft phone cases |
| 95A | Firm flex | Most hobby uses, wheels, general cases |
| 98A | Slightly flexible | Semi-rigid parts, snap fits |
For most hobby printing, 95A is the practical default. It's flexible enough to be useful and firm enough to feed reliably. Softer variants (85A and 90A) are harder to print because they buckle more easily between the extruder gear and hotend. If you want to try very soft TPU, a well-dialled direct drive printer is basically required.
Troubleshooting TPU Problems
Filament grinding in the extruder:
The gear is chewing through the soft filament instead of pulling it cleanly. This happens when print speed is too high or retraction is pulling the filament back into the drive mechanism where it buckles. Reduce speed and cut retraction to near zero.
Inconsistent extrusion and skipping:
The filament is buckling somewhere between the extruder and nozzle. On direct drive printers, check that the PTFE tube is fully seated against the nozzle with no gap. Even a 1-2mm gap gives the soft filament room to bunch. On Bowden printers this problem is essentially inherent at anything above very slow speeds.
Parts too stiff after printing:
Increase infill percentage, or switch infill pattern. Gyroid infill in TPU produces noticeably different flex characteristics than grid infill. Gyroid is generally better for parts that need uniform compression in all directions, like cushioning or vibration dampeners.
Parts feel brittle or crack when flexed:
Almost always wet filament. TPU absorbs moisture fast, and prints that were flexible when fresh become brittle as the material breaks down from moisture exposure. Dry at 45-50°C for 4-6 hours and reprint.
Summary
TPU is rewarding once dialled in. The key rules:
- Slow down - 25mm/s, no exceptions until you know your setup
- Minimal retraction - 0-2mm direct drive, 0-1mm Bowden
- Direct drive printer is much easier than Bowden
- Keep it dry - store with desiccant
Start with a simple test print - a small cube or a phone case - before attempting anything complex. Once you've got clean TPU prints, you'll wonder how you managed without it.
