I wore the shirts on vacation, which included a LOT of swimming and hiking. Didn’t get burned at all. The long sleeve, high neck shirt is like a rash guard, but not as form fitting, so it will be a bit floppy while you swim. TUCKITIN! I wore a bikini top under mine and it was just fine, and I didn’t tuck it in. I swam by the beach, snorkeled after being dropped off in the middle of the ocean by a boat, and I didn’t have any problems with it. I wore the V neck ¾ sleeve during the day, as casual wear, while sight seeing. I was in the burning sun, in Costa Rica, St. Barts, St Maarten, and the shirts really helped. They do get fuzzy if you rub against things or get velcro stuck on them, but so does any bathing suit. I’m very happy with my purchases, and the shirts I got a year ago are still going strong.