I ordered these, although no sizing detail is given--really, who needs chest and waist size to get arm coolers. I laughed when I pulled them out of the bag. I have small arms and have worn compressive clothing but these take it all to another level. The important info was on the box, which recommended 8" upper arm circ. and 4.5" wrist circ. (S), 8.75 and 5.25 (M), and 9.5 and 6.0" (L). I think the issue is the lack of stretch overall to make the compressive fit, unlike CEP and CW-X, which are able to stretch more while still being compressive. I measured the TYR coolers myself and got 4.25" and 2.5". That means it takes a lot of stretching to go from 4.25" to actual 8" arm size, and 2.25" to 4.5". I also measured new Louis Garneau and Sugoi coolers in small (which fit me just fine): measurements are not that different, but the fits are entirely different. The LGs measured 4.5" and 2.5", and the Sugois 4.5+ and 3". I gave the TYR coolers a bad rating because of the lack of info and high price, even though they seem well made. I'm sure some would love them, but not what I was looking for.