About one year ago I did some tests printing with TPU, just to get a grip on it.
I kept the printed parts (failures in fact) on a shelf for no reason.
None have being hit by direct sun light, just indirect daylight and by night LED bulb light.
At the printing time the TPU was quite elastic, I could of made a slingshot of it and probably I could manage to shoot up to 10 meters (some real rubber shoots up to 50 meters), touch in hand while banding the parts it felt pretty elastic, almost like rubber, it came back in original position almost instantly when bent. Cutting the supports with scissors felt like cutting through a sheet of super elastic rubber.
One year later I grabbed them to cut some of-cuts for a buffer I needed on the printer, and to my surprise they were more rigid than I remembered, still elastic, but stiffer, returning back slower, and when I have cut the parts with scissors it could feel the rigidity. I think without doing any rigorous tests that some half of the elasticity is gone. Probably as a sling shot it would not even thrown one meter away.
Make me think,maybe I should test TPU after printing with some precise method, leave it on a shelf in direct atmospheric conditions and another batch in a room in the dark for one year and try that again too see the differences.
Anybody knows more about TPU here?