Acid Free foam board protects and preserves artwork, photographs, certificates, maps and documents. The smooth, bright white surface has a slightly glossy finish that easily accepts markers, crayons, paints and adhesives. Will not become weak, brittle or yellow with age and is pH neutral. Lightweight and rigid, foam board cuts easily with a knife or razor. Boards measure 20" x 30" with 3/16" (5mm) thick, dense white polystyrene foam core and white on back of sheet. 25 sheets per carton.