95% cotton 5% spandex Sizing Tip: Just take one of your own similar style tops, lay it flat, and measure straight across from armpit to armpit.  Then compare to the measurements provided in the description. Please see measurements for sizing. Approximate Measurements (lying flat, no stretch): Small Armpit to armpit- 14" Length- 24" Medium Armpit to armpit- 15" Length- 24.5" Large Armpit to armpit- 16" Length- 25"