FDM with TPU – Flexible Parts with Precise Hardness

TPU (thermoplastic polyurethane) is the filament that opens the FDM world to products that otherwise require injection-molded rubber: phone cases, grips, flexible tubing, medical orthoses, watch bands, dampers. TPU comes in different Shore A hardness, from 60A (very soft, rubbery) to 95A (semi-rigid, leather-like). For FDM, 95A is easier (prints like a viscous PETG), 60A needs a special printer with direct drive and tight idler. This guide shows how to dial a printer for TPU, which printers handle it, and when TPU is the right choice over alternatives like flexible resin or silicone.

Which TPU hardness?

TPU is measured in Shore A: scale 0 (super soft) to 100 (rigid). For FDM, three hardnesses are realistic:

Shore 95A: almost PETG-like. Can print on Bowden and Direct Drive. Suitable for: keychains, flex enclosures, dampers with high duty. This is BEGINNER TPU.

Shore 85A: more flexibility but needs direct drive and weak idler tension. Suitable for: phone cases, yoga blocks, ergonomic grips. This is INTERMEDIATE TPU.

Shore 70A or 60A: extremely soft, rubbery. Needs a specialized printer (Bambu X1, Prusa MK4 with druckhead modification). Suitable for: gaskets, medical orthoses, bicycle grips. This is SOFT TPU and not recommended for beginners.

For most hobby applications, 95A is the optimal choice. Start with it and move to softer when you have experience.

Recommended FDM printers for TPU

Bambu Lab X1-Carbon (€1449): optimal for TPU. Direct drive extruder, AMS support for TPU (AMS doesn’t recommend TPU below 80A as it can retract).

Prusa MK4 (€999): direct drive with modified Bondtech BMG extruder, good flow control for TPU. Recommended for most TPU hardnesses.

Bambu Lab A1 (€420): direct drive, good for 95A TPU. For softer 85A it can struggle, but 95A prints cleanly.

Avoid: Bowden printers like stock Ender 3, Bowden tube for TPU 85A or softer is impossible. You can upgrade to Direct Drive for €60-€100, then it works.

Creality K1 Max: direct drive, good speed, but the heated chamber softens TPU too quickly. Disable chamber heater for TPU prints.

Recommended TPU brands

NinjaTek NinjaFlex (85A): pioneer of FDM TPU. Premium price €45-€55/kg, but layer adhesion and tear resistance are exceptional.

NinjaTek Cheetah (95A): easier version of NinjaFlex. Recommended to start. €40-€45/kg.

Polymaker PolyFlex TPU95: €30-€35/kg, more affordable. Slightly less elastic than Cheetah, but quality.

Fiberlogy Fiberflex 40D (95A): good layer adhesion, Polish brand, €28-€32/kg.

Bambu Lab TPU 95A: optimized for Bambu direct-drive printer. €30/kg. Recommended if you have a Bambu.

Avoid: unbranded TPU. Different batches show 0.2 mm diameter differences: no printer can compensate.

Optimal settings for TPU 95A

Nozzle temperature: 220-235°C. Start at 225°C. Higher temperatures make TPU more flowable (potential stringing).

Bed temperature: 50-60°C. TPU doesn’t warp, so hot bed isn’t critical. PEI sheet or painter’s tape work well.

Speed: 20-40 mm/s. TPU doesn’t print at high speed: flexible filament doesn’t transmit push force well through a Bowden tube. Direct Drive allows up to 60 mm/s.

Retraction: MINIMAL. 0.5-1.5 mm. Higher retraction for flexible filament causes under-extrusion. Speed 25 mm/s.

Cooling: 50-100% after the first 2 layers. Cool fan helps detail with fine features.

Layer height: 0.20-0.25 mm. Thin layers (0.10 mm) for TPU are difficult: layer adhesion suffers.

Infill: 20-40% gyroid or cubic for most TPU parts. Higher infill for tough applications. TPU 100% infill is realistically possible: part becomes rubbery but indestructible.

First layer: slow (10 mm/s), no cooling, normal Z-offset.

Common mistakes

Stringing: TPU is known for stringing. Solution: lower nozzle temperature by 5°C, raise retraction speed to 30 mm/s, enable coasting in slicer.

Filament jam: soft TPU can block filament guide tube. Solution: limited retraction (no more than 2 mm), direct drive setup, dried filament (4 hours at 50°C). TPU absorbs moisture quickly: store in box with silica gel.

Under-extrusion: flex filament idler is too loose. Tighten idler. Not too much: TPU crushes easily.

Layer separation: raise nozzle by 5°C, lower cooling in first 5 layers, slow first layer.

Part deformation: TPU 85A or softer partially deforms under its own weight during print. Solution: pyramidal supports, slower print, or print with rigid support material PVA.

Frequently Asked Questions (FAQ)