I go for runs in the hot desert sun, and sunblock is not enough to protect my very fair skin. These arm sleeves are perfect, and if you wet them down, they are cooling, as well. I tested them by putting a bandaid on my arm, then covering up with these sleeves and going out for a run. When I got back, I took the sleeves and bandaid off, to see if there was any suntan indication that there had been a bandaid there. (If sunlight got through the sleeves, there would be a line around the bandaid.) ThSee full review