Amazon.com: Rit Sun Guard Laundry Treatment UV Protectant ...
Very easy to use -- just use one packet for a normal-sized load of laundry. Water must reach 100 degrees F and wash cycle must be at least 15 minutes long. One treatment is good for 20 washes. It only improves the UV protection of NATURAL fibers. Boosts the UPF of your clothing (UPF is a different rating system for clothing) from UPF 5 to UPF 30.