This is a case of 4 pieces of 24 x 48 x 2 inch Rockboard 60, manufactured by Roxul. It is rigid mineral wool board with a density of 6 pounds per cubic foot. Rockboard 60 is a great option for acoustic projects that require a rigid material. Its also used in some bass trap designs. PRODUCT SAFETY INFORMATION – Warning: Can cause respiratory, skin and eye irritation. Precautionary Measures: Avoid breathing fiberglass dust and contact with eyes or skin. Wear long-sleeved, loose fitting clothing, gloves, respiratory, and eye protection when working with this product.