sun protection

Can anyone recommend some outwear designed to filter sun's rays? I am training for RAGBRAI, but I know from past experience that too much exposure to the sun will give me problems. Of course I will use sunscreen, drink plenty of water and all those sensible things. But I'm wondering about the lightweight shirts I've seen advertised that will filter the sun's rays. Do these work? Do they breathe? Can anyone comment on pros/cons of using them on a long ride?

http://forums.teamestrogen.com/showt...ght=protection

here's another thread about the same thing with some links to summer sun wear. Good luck with the RAGBRAI