I have several of these and they are my favorites. The material is comfortable, breathable and durable (I had my first Riftline polo shirt at least two years ago and it still looks great). I'm 5'6", 150 pounds, have a slim, athletic build, and a perfect athletic (but not tight) fit. I usually wear medium sized shirts for most shirts, so I'd say these shirts run a little big However, I would say that the sleeves are a bit narrower than a regular shirt, so if you have big arms this shirt might feel tight.