This is actually an answer I gave somewhere else in the forum, but it is not the first time I noticed people have a “fear” of using TPU, so I turned the answer into a little topic of its own.
Sure TPU can be frustrating. This noodle kind of filament tends to escape at the extruder and even so, beside the actual failed print, nothing is lost and you can re-spool it, it can be a hassle.
BUT: TPU is not that hard if you know the facts and rules. This is just my 50 cents of knowledge, which got me to a similar success rate than using PLA or ABS.
Every 3D printer is able to print TPU. It may need a little modification, but this can stay when swapping back to other filaments.
Price:
TPU seems to be expensive at first glance, as the price per gram is higher than with other materials. But your are wrong here. Sure they usually sell 750g spools and they are a little more expensive than lets say PLA, but the main issue is the material density. TPU is lightweight. So even a spool only has 750g you may get the same amount of filament, when it comes to length.
So the slightly higher price is coming from higher production costs and the lower sales rate. If I remember correctly the difference at my local filament store is around the same as for glow in the dark or other specialized stuff and about 4 euro or so.
Also keep in mind that you (usually) don´t print giant objects. I have my spool for about 6 years now. Yes, just one spool. But I printed to many functional parts with it. Sure if I would print just dragons and statues it would run out as fast as other materials, but well I don’t. 
TPU is absorbing water:
TPU filament is absorbing moisture from the air. Well, this is true. I think. Fact is in all those years I own and use this single spool of TPU filament I never put it into a sealed box or dried it (even so I build a dryer for filament). It was stored in the opening like any other filament. (ABS/PLA). Even after about 6 years I have no issues with it.
However. This is northern Germany and not Florida. Also the filament brand has probably a huge impact on that, so be prepared to need a dryer.
I am noticing that the first few centimeters of PLA filament (10-15) are getting brittle in about a week, but the rest just prints fine. TPU does not get brittle, so maybe the first centimeters are moist and I simply don’t noticed it yet, as it is used for the brim or so. The spools are stored in the open on a shelf next to my printers in a dry and (during the winter) minimal heated room inside my house. Maybe storing my stuff in the garage would result in a different result.
Just be warned. If you hear noises like little bubbles bursting and the print has little gaps in it, your filament need to be dried.
What else is required?
You should have a direct extruder. Bowden is not a deal breaker, but creates more issues with retracts and requires a very narrow extruder outlet (see next point) or the filament will escape there as push forces fire back.
Your extruder should also have next to zero space between the extruder gears and the inlet/outlet. If you look from the side onto your extruder gears there should only a minimum amount of filament being visible before and after the gears. You can print little triangular inserts to glue into those areas if needed, to fix the problem. Preferable in ABS/PETG as the extruder motor is getting hot during prints. They can stay installed, when printing other materials and should even make inserting any material much more easy.
It is also useful if your extruder has a tensioning screw. If the gears are set to strong, TPU wants to go even sideways between the gears, when the pressure is to strong, while other materials grind. My TronxyX5s for example has an extruder spring utilizing a screw (basically the screw head insert) I need to remove. This results in giving the spring 4-5mm more room to expand and lowers therefor the tension. This extruder tension is probably more problematic than the gabs I mentioned before and after the outlet and inlet. TPU does not like to be squeezed. Like a stress ball it tends to find its way to escape the force.
What are the most required print settings?
Just set print speed to around 50% of your normal configuration (25-30mm/s), turn off supports and you are good to go.
Speed and support wise you can go up later on. Start with the basics for maximum success.
If you run into trouble also deactivate retraction.
You can use supports, but be aware you need a sharp knife and therefor an opening to access the area to clean.
A brim is possible increase layer adhesion, but the rule about cleaning applies here, too. I find the best way to cut of a brim is using scissors. TPU layers are bond like hell. If you print a timing belt, don´t be surprised if it actually works and cannot be ripped apart without massive force.
A raft is a no go. It will impossible to be removed.
Depending on the type of filament and the infill the squishiness is set. Use at least two or three walls. This makes the object robust. The less infill you use the more squishy the part gets. This is actually a good and probably the only situation calibration cubes can be handy to find your personal infill settings for different use cases. A more stiffer door bumper, but a less stiffer wallet print.
Is bed adhesion a problem?
When printing on glass or similar you need glue stick. I use cheap “UHU Stic”. One layer of glue is enough for at least 5-10 prints.
So if the print gets loose do that for your print surface, too.
Some links for upgrading your printer.
First a replacement of an extruder part with great images of where the TPU problem is: Ender-3 TPU Extruder Fix by exeswizz - Thingiverse
There is an image showing the filament path and a red line, where the gab is closed. Don´t get confused here. The bottom side is usually covered by the motor gear, when mounted and was removed as the before/after images where taken flat on a table. Keep in mind that extruder parts should never be printed with PLA due to the heat constantly radiating on the part. PLA will soften over time and very slowly. You don´t want to end up a 12 hour print because your extruder is melting.
Second the insert I talked about above: (these are not the exact the ones I used for my GeitPrinter, but similar ones)
You will probably find a matching part for your extruder when searching. Those are available for more or less every printer and/or extruder. Luckily my TronXY X5 has this little triangular guide build in. It could be a little bigger, but it works as it is.
What to print?
TPU is a great stuff to play with and there are so many things you can print with it. I created door bumpers, towel holders, hose adapters, protective dust inserts and there is so much more like: rubber feed, protective furniture corners, wallets, rubber washers … The flex(ibility) is key here. If PLA or other stuff is breaking, try TPU.
I hope I was able to shine a little light onto this cool and functional filament, so you give it a try.
Happy 3D Printing
