TPU, or thermoplastic polyurethane, is a really great 3D printing material to work with. TPU allows you to create an almost rubbery product can move and be squeezed and squashed and crushed in all kinds of different ways. There are, however, a few challenges with TPU. Since it's a soft material, it can be very difficult for 3D printers to work with it, because as the machines push filament back and forth, the material naturally bends and moves around.
The first thing to do if you're working with TPU is try to use a Direct Drive extruder. Direct Drive machines have a lot less chance for the filament to jam or bow or bend or compress in such a way that it jams up the machine. Very often, Bowden extruder machines end up jamming. In that long Bowden tube, the filament has to be compressed like a spring being squashed and going out sideways, so it grabs onto that tube and is really difficult to control. Therefore, if you can get a direct drive machine, use the direct drive machine.
The second thing to do is run your machine slowly. Again, since the filament is soft and squashes like a spring, you should give your machine time to extrude very slowly. If it extrudes too quickly, the TPU won’t come out smoothly. The first step is to slow down your print speed. Then, if you're using retractions, have a fast retraction. Lastly, if your slicer permits it, have a really slow prime as well. That way, you’ll have time to reload the nozzle, and the filament is able to recompress and reach stasis again. If you go fast, then you're going to end up with gaps in your print.
The last thing to be concerned about is the connectivity between layers. When using TPU, especially when slowing down print speeds, it sometimes has difficulty connecting in between layers. If you want your TPU parts to be a little bit stronger through the layers, turn off the cooling fan and that will allow those layers to adhere to each other much better.
TPU is a great material with its very high temperature resistance and its superior rubbery flexibility. If you accommodate for the material by using a direct drive extruder, slowing down your prints, and turning off your cooling fan, it can be a very useful material.