TPU filament: hardness, print settings and flexible custom parts
TPU becomes useful when a part needs to give: a phone case during installation, a protective cap around a profile or a compliant contact area between components. Flexibility creates opportunities while placing different demands on design and filament feeding.[1]
The useful question is therefore how the finished part should behave. A thin case wall and a solid bumper can feel very different even when printed from the same spool.
What is TPU?
TPU stands for thermoplastic polyurethane and belongs to the thermoplastic elastomer family. Flexible TPU filament can be processed by FDM printing. The compliance wanted in the finished part also creates challenges while feeding the material.[1]
Material identity, hardness and product profile belong together. Choose a clearly identified product for a controlled trial and record its manufacturer. This lets you evaluate later changes without introducing several unknowns at once.
Shore hardness: what do 85A, 95A and 98A mean?
Shore hardness describes resistance to indentation by a test instrument. Within the same Shore A scale, a higher value indicates greater hardness. It does not determine how easily your finished case will bend on its own. Wall thickness, shape and internal structure also matter, as Polymaker explains in its TPU guidance.[2, 3]
| Label | What it tells you | What remains unknown |
|---|---|---|
| Lower Shore A value | A tendency toward softer material within the same scale | Stiffness of the actual printed part |
| Higher Shore A value | A tendency toward harder material within the same scale | Whether case installation and retention improve |
| Same value on two products | The same nominal hardness label | Whether formulation, print behavior and recovery match |
| Shore D value | A different hardness test scale | A direct numerical comparison with Shore A |
98A versus 95A does not provide a simple percentage increase in part stiffness. If you want something firmer than your current TPU, examine the existing geometry first, then compare another hardness or formulation deliberately.
Wall design changes the result
Imagine a thin open strip and a thick closed ring made from the same spool. They will deform differently. The material has stayed the same; the construction has changed.
For a phone case, consider the back, sides and corners separately. A thin back may flex while a stronger rim determines retention. For a softer bumper, internal structure may have a greater role.[3, 4]
Inspect the slicer preview. A thin case wall may already consist entirely of perimeter lines. Changing infill percentage then has little or no effect in that area. Check the generated paths instead of assuming the numerical setting changes the part.
TPU settings: two product examples
TPU needs a profile matched to the actual filament. This table shows manufacturer specifications for PolyFlex TPU95 and Prusament TPU 95A. They are product examples, not a universal TPU range.[2, 5]
| Setting | PolyFlex TPU95 | Prusament TPU 95A |
|---|---|---|
| Nozzle | 210–230 °C | 220–240 °C |
| Bed | 25–60 °C | 55–75 °C |
| Speed | Manufacturer specifies 20–40 mm/s | Use the appropriate slicer profile |
| Cooling | Manufacturer specifies cooling on | Use the appropriate slicer profile |
Do not transfer retraction values blindly from another extruder. Start with a suitable profile and check for consistent feeding. With elastic filament, resistance along the feed path can be as relevant as a slicer setting.
A high-flow TPU is a separate product. You cannot compare its processing speed with ordinary TPU95 solely by looking at hardness.
Check feeding and build-plate compatibility
Plan a low-resistance path from spool to extruder. Check that the spool turns freely and that the printer supports the chosen TPU. Use an automatic material feeder only when the exact system and filament combination is approved.
“My printer can print TPU” does not settle that additional question. A product explicitly designed for one automatic feeder does not establish compatibility for other TPU formulations.
The particular material and plate combination matters too. Prusa warns that Prusament TPU 95A can adhere excessively to smooth PEI without a separation layer. Follow your plate guidance before printing a large case back.[5]
Practical example: refine a phone case in two trials
Start in the Phone Case Generator with the appropriate device model or verified device measurements. Choose the TPU profile and a simple back design so that fit and material behavior are easy to assess initially.
First trial: fit and installation. Use the generator's short fit test. Check whether you can install it without excessive force, whether the edges sit against the device and whether retention is sufficient. Revise a section that needs substantial stretching before printing the complete case.
Second trial: desired firmness. If fit is broadly correct but the case feels too soft, change one geometry variable first, such as side-wall thickness. Comparing a local 1.6 mm wall with a 2.0 mm version is a suggested experiment, not a validated preset for a particular phone.
Keep filament, orientation and profile unchanged for the comparison. If the geometry trials do not reach the desired range, try another hardness or formulation. Recheck fit after the material change.
On the complete case, also check buttons, charging access, camera opening and screen rim. A comfortable fit does not establish a tested drop-protection rating. A successful fit prototype and demonstrated damage protection are different outcomes.
Flexible end caps and contact areas
The End Cap Generator also lets you try a compliant cap. First decide whether it goes over the outside of the profile or inserts into it. Those versions use different measurement references.
Begin with a short section whose wall and engagement depth you can evaluate easily. Check its fit after installation and again after some time. For a continuously loaded cap, in-use deformation belongs in the assessment.
TPU does not automatically qualify a part as a seal. A soft cap may conform well and still leak through a seam or defect. A functional seal needs a suitable combination of material, medium, geometry and operating conditions.
Moisture and storage
If a print develops bubbles, a rough surface or unusual stringing, moisture is one possible cause. Check the temperature profile as well. For its TPU 95A, Prusa specifies at least four hours at 60 °C when drying is needed. PolyFlex TPU95 lists 70 °C for eight hours when the material has absorbed moisture.[2, 5]
These differences are a good reason to follow the actual product. Also consider the spool's temperature tolerance and the dryer instructions. Drying and dry storage complement each other but are different processes.
Common TPU problems and useful first checks
| Observation | Useful next step |
|---|---|
| Filament buckles during feeding | Check feed path and extruder according to the device manual; use an appropriate flow rate |
| Print contains gaps | Check consistent feeding and nozzle condition before raising extrusion flow |
| Surface contains bubbles | Check filament condition and temperature |
| Excessive stringing | Retest with a suitable profile and dry material |
| Overhangs collapse | Change orientation or shape and reduce unsupported regions |
| Case feels too soft | Inspect generated wall paths and geometry; then consider a different hardness |
| Case fits too loosely | Adjust the fit dimension deliberately rather than changing all wall dimensions at once |
Manufacturer guides address several of these symptoms. The exact remedy must suit the printer; a screw adjustment for another extruder is not a universal TPU rule.[1, 5]
Related generators
Frequently asked questions
Which TPU hardness works for a phone case?
95A is a common starting class. Whether it feels firm enough depends on the product and case geometry. Test a short section first. Compare construction or a harder product deliberately rather than treating one Shore number as a guarantee.
Is there something between soft TPU and PETG?
Investigate harder TPU formulations. The categories are not a uniformly spaced material ladder. A thin part made from a harder plastic and a thicker TPU part can feel different while also having different assembly and recovery behavior.
Does 100% infill make TPU rigid?
It changes the internal structure where the model actually has an infill region. It does not turn the elastomer into an identical substitute for PETG. Thin case walls are often governed more directly by their wall construction.
Can I use TPU with any automatic filament feeder?
Only use an explicitly supported combination. Check the exact feeder and filament specifications. Hardness alone does not demonstrate compatibility.
Must TPU always be printed very slowly?
Many ordinary flexible filaments need a controlled, relatively low flow rate. Specialized products may be formulated differently. Use the matching manufacturer profile instead of applying one fixed speed rule to every TPU spool.
Is TPU automatically skin-safe or food-safe?
The material name does not approve every contact application. Check explicit documentation for the actual product and the intended finished object.
Next step: Configure a phone case and print the fit test.