Mineral Paper is composed of 80% calcium carbonate for a unique surface suitable for water based paints or alcohol inks. These Mineral Paper boards are made with 150 gsm mineral paper mounted on a hard backing board to provide a unique, sturdy substrate that will not stretch, tear or warp. The Assorted pack of 3 includes one each of 5 in. x 7 in., 6 in. x 8 in. and 8 in. x 10 in. boards.