I got a size Large and it works. The material inside is the neoprene and it feels great working out or just walking. Keeps my knee aligned safely, there is no pain or pressure while wearing this and it makes life really easier for me getting around. The cold weather bothers my knee, however, I can wear this and be mobile longer with it on. The straps being adjustable allows me to loosen while relaxing, or tighten up when I am standing for longer periods of time and walking around, so there is no sudden offset by my knee, no popping or cracking to it. I am quite satisfied having this around for use.