The complete guide to printing flexible filament on your Bambu Lab P1S — external spool setup, 4-way splitter routing, slicer settings, and troubleshooting from real user experiences.
TPU (Thermoplastic Polyurethane) is a flexible, rubber-like filament that opens up an entirely different world of prints — but it requires a fundamentally different approach than PLA or PETG.
A thermoplastic elastomer that combines the flexibility of rubber with the processability of plastic. When printed, it creates parts that bend, stretch, compress, and bounce back — like printing your own rubber.
TPU is soft and compressible. Where PLA acts like a rigid rod pushed through the extruder, TPU behaves like a wet noodle — it can buckle, wrap around gears, and jam if you push too hard or too fast.
The AMS feeder gears compress TPU instead of gripping it. The long Bowden path through the AMS buffer gives TPU too much room to buckle and bind. External spool feeding is mandatory.
Shore A measures how soft a flexible material is. Lower = softer. Most TPU filament is 95A.
Phone cases, tablet bumpers, laptop corner guards, drone bumper mounts, electronics enclosures with shock absorption.
Watch bands, shoe insoles, custom orthotics, flexible bracelets, grip wraps for tools or gym equipment.
Gaskets, O-rings, vibration dampeners, flexible hinges, cable strain reliefs, belt clips, spring mechanisms.
Everything required for TPU printing on the P1S with an AMS installed.
This is the part that confuses everyone. Let's break down exactly what connects to what and why.
Right now, your filament takes this path from spool to nozzle:
With the splitter, you merge both the AMS path and an external spool path into one output that feeds the extruder:
Step-by-step setup of the 4-way splitter with your AMS and external spool dryer.
Find the PTFE tube that goes from the AMS buffer into the top of the printer (the extruder filament inlet). Press the blue collet fitting and pull the tube out of the printer's inlet. This tube will now go to the splitter instead.
Take the tube you just disconnected (coming from the AMS buffer) and insert it into Input 1 of the 4-way splitter. The AMS side stays connected — you're just adding the splitter in between.
Cut a new piece of PTFE tubing and run it from the output of the splitter down to the printer's extruder filament inlet (where the AMS tube used to go). Keep this tube as short as possible — every extra centimeter adds friction for TPU.
Run another PTFE tube from your filament dryer's output hole to Input 2 of the splitter. Again, shorter is better. Avoid sharp bends — TPU will buckle at tight curves.
Position the splitter somewhere accessible — the back of the printer, a side bracket, or a 3D-printed mount. Many users print a bracket that clips to the printer frame. Make sure the tubes have gentle curves, no kinks.
Place your Sunlu TPU spool into the filament dryer. Set it to 50–55°C and let it dry for at least 2 hours before your first print. Thread the TPU end through the dryer's output hole.
Manually push the TPU filament from the dryer output → through the PTFE tube → through the splitter → down into the printer until you feel the extruder gears grab it. You should feel slight resistance when the gears catch. Don't force it — if it won't go, check for kinks or tight bends.
On the P1S touchscreen: go to the filament/material settings and select External Spool. Set the filament type to TPU. This tells the printer to use the extruder motor to pull filament rather than waiting for the AMS to push it.
These settings are compiled from hundreds of real user reports on Reddit, the Bambu forum, and MatterHackers. Start here and fine-tune from this baseline.
Run through this before every TPU print. Check items off — your progress saves automatically.
Every issue here is something real P1S users have encountered and solved. Severity indicates how likely it is to ruin your print.
| Problem | Cause | Fix |
|---|---|---|
| TPU jams in extruder | Speed too fast — TPU buckles under pressure instead of flowing | Reduce print speed to 30mm/s. Lower volumetric flow to 3.0 mm³/s. Check for kinks in the PTFE path. |
| TPU wraps around extruder gear | Retraction too high — filament pulls back past the gear teeth | Reduce retraction to 0.4–0.8mm. Some users disable retraction entirely. Make sure you're using Generic TPU, not TPU HF profile. |
| Stringing everywhere | TPU is inherently stringy — the material stretches instead of breaking cleanly during retracts | Lower nozzle temp by 5°C. Disable z-hop. Enable "avoid crossing perimeters." Set print sequence to "by object." Clean up strings with a heat gun on LOW after printing. |
| Poor bed adhesion | Bed too cool, dirty surface, or wrong plate type | Use textured PEI plate at 35–50°C (best for TPU). Clean with IPA. Apply glue stick on smooth PEI. Slow down first layer to 15mm/s. |
| Elephant's foot (first layer too wide) |
Too much squish — nozzle too close to bed | Raise Z offset by 0.02–0.05mm increments. TPU is soft so it squishes more than PLA at the same Z height. |
| Buckling in PTFE tube | Tube too long, sharp bends, or too much resistance in the filament path | Shortest possible PTFE path with gentle curves. No kinks. Use Capricorn tubing for lower friction. Make sure the spool spins freely. |
| Under-extrusion | Filament moisture, nozzle temp too low, or partial clog | Dry TPU at 50°C for 4+ hours. Increase nozzle temp by 5°C. Do a cold pull to clear any partial clogs. Run flow calibration. |
| Layer delamination | Nozzle temp too low — layers aren't bonding | Increase to 230°C. Reduce fan speed to 50%. TPU needs enough heat for interlayer adhesion. |
| Print won't stick to PEI | Wrong plate or surface prep | Textured PEI works best. On smooth PEI, apply a thin layer of glue stick. Some users run the bed at 55–60°C for smooth plates. |
| Popping/sizzling during print | Wet filament — moisture boiling inside the hotend | Dry the filament! 50–55°C for 4–6 hours minimum. Feed directly from the dryer during printing. Store TPU in sealed bags with desiccant. |
| TPU won't feed from dryer | Spool resistance or tangled filament | Make sure spool rotates freely in the dryer. Check for tangles or crossovers on the spool. The extruder can't pull hard enough to overcome high resistance. |
Designing for TPU is different from designing for rigid filaments. Here's what works.
Use thin walls (0.8–1.2mm) where you want flex, and thick walls (2mm+) where you need rigidity. The wall thickness controls flexibility more than any slicer setting.
TPU excels at living hinges — thin sections (0.4–0.8mm thick) that flex repeatedly without breaking. PLA snaps after a few bends; TPU survives thousands.
Gyroid or lattice infill makes parts uniformly flexible in all directions. 10% infill = very bendy. 50% = moderately stiff. 100% = solid rubber. Experiment to find your sweet spot.
Wall count affects flexibility more than infill percentage. 2 walls with 20% infill feels very different from 4 walls with 20% infill. More walls = stiffer.
TPU has lower detail resolution than PLA. Avoid features smaller than 1mm. Text should be at least 8pt. Small holes may close up — oversize them slightly.
Add fillets (rounded edges) everywhere. TPU doesn't print sharp internal corners well — they tend to bulge or collect strings. 0.5mm+ fillets on all edges.
TPU prints need different cleanup techniques than rigid filaments.
Quick passes with a heat gun on LOW setting. The strings melt and shrink away. A lighter works in a pinch but risks scorching. Don't use a hair dryer — too diffuse, takes forever.
Scissors beat flush cutters. TPU deforms under the pressure of cutters instead of cutting cleanly. Sharp scissors or a craft knife work much better for trimming brims and small imperfections.
Freeze the part first. Put it in the freezer for 30 minutes — TPU becomes temporarily rigid when cold, making supports much easier to snap off. Peel supports while the part is still cold.
TPU can't be sanded like PLA. Light sanding with 400+ grit works for minor imperfections. For a matte finish, a very light scuff with a Scotch-Brite pad works well. Don't use acetone — it doesn't affect TPU.
Now that you know how to print TPU, here's what to make with it.
Measure your phone, design in Fusion 360. Thin walls for flex, thick corners for drop protection.
Custom fit, custom color. Print flat with living hinges at each link point.
Dampen your P1S vibrations with custom TPU feet. Simple cylinders with 20% gyroid infill.
Custom-sized seals for any application. Print at 100% infill for rubber-like density.
Protect charging cables from bending at the connector. Simple cone shape, 95A is perfect.
Custom grips for game controllers, bike handles, or tool handles. Textured surface for grip.
Protect laptops, tablets, or drones with corner bumpers. Thick walls, low infill for shock absorption.
Phone/tablet stand that folds flat. Living hinge design with rigid sections.