This shirt is so comfortable! Ran a marathon wearing it. Zero chafing. Stayed warm during the cold weather in the morning (low 40s) and even though the sun came up and it warmed up to low 70s, I was still comfortable. Just had to lower the zipper and felt fine. True to size. I'm 5'7 and about 140 lbs. and got a Medium. Highly recommend it. I ordered a second one in another color because I love it so much.