While it's certainly turning into a great industry, UV resistant clothing is pretty much unnecessary for most people, as virtually all fabric that isn't see-through does a reasonably effective job blocking UV. Research shows white t-shirts have an SPF of 7, while darker colors are around 10. If you wear an undershirt and something over it, you're pretty well protected without any special clothing. Common sense tells you the biggest problem is caused by unprotected skin, not by people's clothes letting them down. After all, when was the last time you burned or even tanned noticeably under your clothing?