I'm 5'1", 160 lbs and have a moderate build. I recently bought this shirt to wear to the pool so I don't have to put on as much sunscreen. , and very similar to most medium sized shirts I own. The material is very light, breathable and very comfortable. It's probably a bit cooler for me to wear this long-sleeved shirt than even a short-sleeved shirt because I'm protecting my skin from the sun's rays. I wore it in the pool for about 3 hours and didn't notice any extra tan on my skin as a result. I'm wearing it in Mexico next week so I'm hoping the UPF will last 50. I also run a bit but haven't worn it for runs yet but my pool experience tells me it will keep you cool as it is very breathable.