I ride my bike all the time, so I'm exposed to the sun for most of the day. Before these shirts, I put on sunscreen four times a day. Pooh! Now I don't know. These shirts will keep you cool on the hottest of days and add a little warmth when worn underneath your winter gear. Despite their low weight, the shirts are hard-wearing. They even appear to be stain resistant. I've bought seven of these so far - all small - and they still look great despite everyday wear. allow thumb holes. For sizing reference, I'm a male, 5'9", 145 lbs, with a 38' chest, 29" waist and 32" sleeves.