Avoid clothes that you can see light through. Remember: If light is getting through, then ultraviolet radiation is getting through, too. The weave of your clothing is also important. The tighter the knit or weave, the smaller the holes and the less UV can get through. Some manufacturers provide extra-protective clothing with UPF (Ultraviolet Protection Factor) labels, which indicate exactly how protective the clothes are: A shirt with a UPF of 45 lets in just 1/45th of the sun's UV.