I was first skeptical because I'm an XS in most places, but I decided I should go for size S. I didn't want a tight fit, something a little loose, this gift from heaven was it. It was a perfect fit, even my girlfriend gave a nod of approval. The shirt rest very lightly on the body, and even on the hottest, humid days of summer it never drastically clung to my body like other shirts I have. Merrell's Optiwick is the real deal. It's the first shirt I've bought from Merrell, and because of the great experience, I've bought more. (This is still my favorite) Note: I bought this shirt over the summer, since then it's gone through the washer multiple times. The shirt is still in very good condition, but the design on the shirt (I got the orange one) has LIGHTLY faded. Emphasis on lightly. The design still very much remains, but now I can't really tell the differences between the runners wearing the sneakers vs the ones with the barefoot shoes. Which definitely is an ice breaker. I've gotten so many questions what my shirt means. Thank you Merrell!