I ride everyday around noon and 3p, so I'm in the sun. Last years (2017) model didn't seem to breathe that well, after a ride it felt like my arms were wrapped in plastic wrap. The 2018 model is much better, it breathe and wicks the sweat. But even after a LONG ride on a sunny day, it still feels good to get the sleeves off. As for sun protection, based on the pale skin after taking my watch off, the sun is still getting through the material, but the arms aren't really dark as compared when I rode without sleeves. I found that pulling the sleeves up the the edge of your riding shirt sleeve, keeps the arm from overheating vs. pulling up to the armpits..