Double layered steel plate, lined with rock wool (mineral wool), handmade. Rock wool, also known as rock asbestos, is mainly composed of basalt. It is a fluffy short and fine fiber made from natural rocks and minerals, and is non combustible. Good fire resistance and high sound insulation performance. Widely used for partitions and ceilings in factories, laboratories, and various places in industries such as food, medicine, electronics, scientific research, aerospace, and pharmaceuticals.