4 mm and 5 mm neoprene blocks the sun pretty well. I'm about to slather up with Neutrogena "beach defense" broad spectrum SPF 70 with "helioplex." Says its water resistant for 80 minutes. Swell period is rather short, so I'll be paddling like some kind of monkey to get back outside after a ride, so 80 minutes is about right. Hey Ive, that Banana Boat Kids sounds pretty good, but please read the label and make sure that it doesn't have any "vitamin A palmitate" in it. I have read that it is an ingredient that may make some people's skin more susceptible to burning and cancer if its applied before one goes out in the sun. Its one of those things that one should apply afterwards, when one is going to be in the shade. I read the label on my tube of Banana Boat, saw that it had vitamin A palmitate in it, and then tossed it in the trash. Then I bought 3 different containers of Neutrogena, each a little different. SPFs 45, 70, and 100. I also bought some Bullfrog SPF 50 that has a lot of titanium dioxide in it, and leaves a white goopy mess on my face, which I often forget about, and then remember is there after I wipe my hand over my nose (only wear that stuff when surfing).