How to 3D print orthotic insoles in TPU: slicer settings step by step
You have the insole design and an FDM printer. Now comes the part that raises the most questions: how to set up the slicer so the insole prints well in TPU. TPU doesn't print like PLA: it's flexible, it absorbs moisture and it doesn't tolerate high speeds.
This guide collects the settings we use as a starting point at Podia3D, based on Bambu Studio's official "Generic TPU" profile. They are starting values, not a fixed recipe: every combination of printer, filament and parameters must be validated with real parts before using it with patients.
If the overall process isn't clear yet, start with the guide to 3D-printed orthotic insoles.
Before printing: printer and filament
The printer. TPU prints much better with direct-drive extrusion (the motor that pushes the filament sits right above the nozzle). With Bowden extruders, flexible filament tends to compress inside the tube and extrusion becomes inconsistent.
Automatic filament changers. Many automatic material systems (such as Bambu Lab's AMS) don't support flexible filaments. In that case, feed the TPU from the external spool.
The filament. The most common TPU grades for desktop printers have a hardness of around Shore 95A. TPU absorbs moisture from the air, and wet filament causes bubbles, stringing and a rough surface. Dry it before printing following the manufacturer's instructions, especially if the spool has been open for a while.
Orientation and plate placement
- Flat, base down. The insole has a flat underside: that's the side that sits on the plate. No supports needed, and the top surface (the one that touches the foot) stays clean.
- Diagonal if it doesn't fit. Large sizes can exceed the side of the plate. Rotated 45°, an EU size 46 fits along the diagonal of a 256 mm plate.
- One insole per plate, or the pair if it fits. Printing left and right together saves machine time.
The build plate
With Bambu's generic TPU profile, the bed runs at around 35 °C. A textured PEI plate works well: TPU grips enough while printing and releases once it cools. On smooth plates, TPU can bond so strongly that it's hard to remove without damaging the surface.
There's no need for a brim: TPU barely warps as it cools, and a brim only adds trimming around the outline.
Slicer settings
These are the starting values, on Bambu Studio's "Generic TPU" profile with a 0.4 mm nozzle:
| Setting | Starting value | Why |
|---|---|---|
| Layer height | 0.20 mm | Good balance between time and finish |
| Walls (perimeters) | 2 | Strong outline without stiffening the edge |
| Top layers | 4 | Closed, even support surface |
| Bottom layers | 3 | Solid base against the plate |
| Infill pattern | Gyroid | Similar behaviour in every direction |
| Infill density | 10–33% depending on firmness | This is what sets the hardness (see below) |
| Supports | No | The flat base doesn't need them |
| Brim | No | TPU barely warps |
| Nozzle temperature | ≈ 240 °C | Generic profile value; adjust to your filament |
| Max volumetric speed | ≈ 3.2 mm³/s | Caps the real speed: TPU doesn't like to be rushed |
The setting people most often overlook is the last one. With TPU, volumetric flow is what limits speed, not the linear speed set for each move. Set it too high and the filament tangles in the extruder and gaps appear. If your filament can handle more flow, the manufacturer will say so.
Firmness: infill density
In a printed insole, the hardness the patient feels depends mostly on the infill, not just on the material. In Podia3D, firmness is prescribed in clinical terms and translated into gyroid infill density:
| Firmness | Infill density | Suggested use |
|---|---|---|
| Soft | 10% | Lighter patients (< 60 kg) or those who prioritise cushioning |
| Medium | 16% | Everyday use, 60–85 kg |
| Firm | 24% | 85–105 kg, or when control matters more than cushioning |
| Extra firm | 33% | > 105 kg, impact sports or maximum rearfoot control |
This is a starting guide, not a clinical rule: final firmness also depends on the specific filament, the insole thickness and your judgement for each patient.
Per-zone firmness. The slicer can apply a different density to one part of the piece using modifiers: for example, a softer rearfoot for plantar fasciitis or a softer forefoot for metatarsalgia. We explain it in STL or 3MF for 3D-printed orthotic insoles: with a 3MF project, those modifiers travel inside the file; with an STL, they have to be added by hand for every print.
Common problems and how to fix them
- Strings between areas. Usually wet filament. Dry it before touching retraction.
- Gaps or incomplete layers. The extruder can't keep up: lower the volumetric flow or the speed.
- Filament tangles in the extruder. Speed too high, or a Bowden extruder. Print slower and check the extruder tension.
- The first layer won't stick. Clean the plate (fingerprint grease is the usual culprit) and check the bed temperature.
- The insole won't come off. Let the plate cool completely before removing it and, on smooth plates, use a release agent.
Validate before using with patients
Before signing off a profile:
- Print a test insole at each firmness level you plan to use.
- Check dimensions and thicknesses against the design.
- Compare flex and feel between levels, and against your usual materials.
- Document the validated profile (printer, filament, settings) and don't change it without validating again.
Documentation is part of the process: in the EU, the insole is a custom-made medical device and the manufacturer must be able to show how it was made.
How Podia3D handles it
In Podia3D, firmness is prescribed per zone (rearfoot, midfoot and forefoot) in clinical terms, and the 3MF project for Bambu Studio and OrcaSlicer comes out with all of the above already set up: TPU, insole placed at 45° on the plate, gyroid, no supports or brim, textured plate and per-zone infill modifiers. All that's left is to slice and print. For PrusaSlicer and Cura it also exports a 3MF with the per-zone infill modifiers; there, material and the remaining settings come from your active TPU profile, so apply the values from this guide to it. And the STL works in any other slicer.
Podia3D is a prototype in its pilot phase and is not certified as medical device software. You can try it now in your browser, no sign-up needed: you start with a sample case loaded, and when you want to export the 3MF or STL, we just ask for your email.