TPU in FDM Printing: Shore Hardness, Settings and Real Applications

TPU is a thermoplastic polyurethane elastomer. In FDM it fills a gap no rigid material can cover: seals, gaskets, dampers, protective covers, bellows, cable strain reliefs and grips. Parts stretch, compress and return to shape. The trade off is that TPU is slower to print, less dimensionally forgiving and far more sensitive to moisture than PETG or PLA.

Shore hardness is the number that matters

TPU grades are described by Shore A hardness. Shore 85A is common for printable filament, Shore 95A is stiffer and easier to process, Shore 60A to 70A is genuinely soft and hard to feed through most extruders. A part printed in 95A feels like a shoe sole. A part in 85A feels like a bicycle inner tube. Choose the grade by the deflection you need, not by the word flexible.

Infill and wall count control the stiffness, not the material alone

The same TPU grade can produce a part that barely bends or one that squashes flat, depending on shell count and infill. A gasket printed with three walls and 100 percent infill is a solid rubber section. The same geometry with two walls and 15 percent gyroid infill acts as a spring. This is useful in production: we tune compression behaviour by adjusting internal structure rather than buying another material.

Why TPU prints slowly

• The filament is elastic, so it compresses in the drive gears instead of pushing forward, which makes flow lag behind the toolpath
• Retraction is unreliable, so stringing has to be controlled through travel planning and temperature rather than large retract distances
• Sharp corners and dense small features need slower speed to keep dimensions in range
• Typical production speed is a fraction of what we run PETG at, which is the main reason TPU parts cost more per unit

Moisture ruins TPU faster than any other filament

TPU is strongly hygroscopic. A spool left open in a workshop for a weekend will print with popping, rough surfaces and reduced tear strength, because water turns to steam in the nozzle and breaks the extrusion. We dry TPU before every production run and print it from a dry box. If you print in house and your TPU parts tear along layers, moisture is the first thing to check, before you change any slicer setting.

Where TPU is the right choice

• Gaskets and sealing lips for enclosures, where a machined or cast seal would need tooling
• Vibration dampers and machine feet
• Protective caps, edge trims and bumpers on handling equipment
• Cable strain reliefs and flexible conduits
• Grips, pads and soft contact surfaces on fixtures that touch finished goods

Where TPU is the wrong choice

TPU is not a structural material. It creeps under constant load, so it should not carry a bolted joint or hold a dimension under permanent pressure. It softens well below 100 °C, so it does not belong near a heat source. For a tough but rigid part use PETG, for wear and repeated deflection use PA12, and for a stiff bracket use PA12-CF. TPU is chosen for elasticity, nothing else.

Design notes before you send a TPU part

• Give sealing surfaces a defined compression, usually 10 to 25 percent of the section, instead of expecting a press fit
• Avoid unsupported spans thinner than about 1 mm, they deform during printing
• Expect slightly larger dimensional variation than in PETG, so avoid tight bores that must fit without adjustment
• Tell us the required Shore hardness or, better, describe how far the part must deflect and under what force

If you are unsure which grade fits, send the part and describe the load case. We print TPU in production every week and will tell you whether an elastomer is even the right answer for your geometry.