... layer is steel sheet,(2) the inner layer is rock wool sandwich,(3) the bottom layer is also steel sheetRockwool density ... steel of panelsLifetime: 15~20 yearsCharacter: Light in weight, heat insulation, fireproof and waterproof, benvironmental Usage: various roofs and ... large size factory buildings, storages, exhibition halls, gymnasiums ,etc Heat insulation and fireproof rock wool sandwich panel