Regular and High Density Fiberboard Insulation Fiberboard Insulation manufactured to a uniform density using cellulosic wood fibers with additives to improve strength and moisture resistance. Each panel is surface treated with a black sealer to promote adherence of the roofing membrane. To learn more about Regular and High Density Fiberboard Insulation, select from the following: Grade Dimensions Standards & Benefits Application Asphalt Application Product Compliance Physical Properties  Return to Roof Insulation