Why do TPU cases turn yellow?

Related questions

1. Do Casemate cases turn yellow?
2. What does TPU mean?
3. What's the difference between a phone case and skin?
4. Does phone case really protect phones?
5. Is TPU foam toxic?
6. What is a tough phone case?
7. Does TPU have BPA?
8. Do wallet phone cases protect your phone?
9. Is silicone a good phone case?
10. Do you really need a phone case?

Tags

1. #after
2. #cause
3. #element
4. #polymers
5. #ultraviolet
6. #course
7. #plastics
8. #yellow
9. #usually
10. #radiation
11. #smartphone
12. #outdoor
13. #because
14. #reason
15. #under
16. #exposes