While not tested out during our blisteringly hot and muggy summers, I wore this yesterday in muggy 85 degree sun on a concrete patio and I don't think I was much hotter than I would be in short sleeves. Plus, I didn't have to worry about all the sweat washing away sunscreen. It does seem to keep me cooler than another sports shirt I have. I do with they had more muted colors, but the purple isn't too bad. If all goes well in June, I will likely order another.