TPU (Thermoplastic Polyurethane) is part of the large family of thermoplastic elastomers, which get soft when heated. It is mentioned separately from TPE as their properties are widely different. TPU is printed at 220-250 °C depending on the composition of the material. It also requires a heatbed that can be heated to 60 °C, and depending on the surface of the heatbed, tape, hair spray or the like may be needed to make the material adhere to the bed.
TPU in hardness and resilience is very similar to rubber, but since it is a thermoplastic, unlike rubber, it can be well used for 3D printing. TPU has a higher abrasion resistance and is more resistant to chemicals, especially oil and grease. Furthermore, it is also resistant to low temperatures, which means that it does not become brittle and difficult to work with. TPU has excellent layer bonding and minimal warping.
TPU is easier to print with than TPE as it is stiffer, reducing the requirements of the 3D printer extruder. However, it is always a good idea to make sure that the filament cannot "escape" along the path to the extruder, especially at the gears that drive the filament. It is also worth making sure that the filament can easily be pulled off the spool, as otherwise the filament can stretch, resulting in under-extrusion of the material.
TPU filament is hygroscopic, which means it absorbs moisture from the surrounding air - it is therefore recommended to store the material in a drybox; a (mostly) air tight container with silica gel in to absorb moisture from the air. If your TPU filament makes little popping noises when it is extruded, the reason is that it has absorbed too much water. This can be remedied by drying the filament in an oven with precise temperature control; such as a food dehydrator, or a dedicated filament dryer.
If you are considering drying it in a conventional oven, it is important to test the stability of the temperature as it can fluctuate quite a bit. This can in the worst case lead to your filament fusing together on the spool.
Depending on how much water the TPU filament has absorbed, it is recommended to dry it for 8-24 hours at 65 °C.
Print slowly, 20-30 mm/s
Turn off retractions
Make sure the filament is unspooling easily
Requires a heatbed
Store dry, preferably in a drybox