Hard skin sponge (1 piece) has double action coarse and fine pored mineral callus sponge. The white side is used to remove tough calluses, welts, and corns from the feet. The finer, blue side is for the hands, ankles, and knees, among other things. The skin becomes soft and velvety once dead skin cells are eliminated. It’s easier to remove calluses with a Gehwol foot bath.