10% spandex 90% organic USA grown cotton. Our spandex is sourced from recycled PET. The straps are made out of 3/4 inch cotton/rubber elastic and cross in the back. We double the fabric in the bra for maximum support for running or stretching. We suggest you choose the same size of pansy bra you would normally wear! It is a snug fit so don't size down unless you want it extra tight! Size up if you want a more lounge crop top fit!