I'm 5'7", just under 160 lbs and in pretty good shape. I bought the small and the medium because that's where I seem to fall in most TS stuff. I ended up returning the medium. There wasn't a huge difference in the 2 sizes but I felt the small just looked more fitted around the thighs. The material is typical bathing suit nylon, but the cut is perfect...at least for me. Not too long or short and usable pockets!