I almost returned it after trying it on. I bought this mainly for SUP. Didn't expect the material to be so heavy and the fit wasn't quite right for my body. I'm 5'11 and 182 lb with somewhat muscular and chest/shoulders and 32" waist. I bought a medium. My perfect fit would have added an inch to the length and more room around the shoulders and chest. Sleeve length is perfect but my armpits seemed tight. Definitely can't wear a t-shirt underneath. I knew it is quality so decided to keep it and tried it yesterday paddling on the Willamette. Temp was in the upper 80s. Glad I kept it. Never felt overheated and barely noticed I was sweating. It was completely dry when I was done which never happens. Didn't feel restricted in the arms like I thought I would. Great quality top. Five stars if it had a liitle more room to wear a shirt under.