Stainless steel and better air flow for faster drying. 

Small (Small Ladies/Child) is 8.5" long from heel to toe and 3.25" wide from sole to insole

Medium (Ladies) is 9.25" long from heel to toe and 3.5" wide from sole to insole

Large (Mens) is 10.25" long from heel to toe and 4" wide from sole to insole