NSN 1560-01-277-1979

An item composed of one or more materials, molded, compressed, and/or baked into a rigid covering of irregular shapes and sizes. it is designed to cover air ducts and/or air duct fittings used in air conditioning, heating, cooling, pressurizing and de-icing systems to restrict the dissipation of heat. it may completely or partially encase the item for which designed. it may be furnished with or without fillers, cement, and/or separate or attached accessories for installation, (excluding flexible air duct covering and rigid pipe and pipe fitting coverings used in construction and building materials). Excludes insulation blanket, thermal, aircraft; insulation pipe fitting covering, thermal; and insulation sleeving, thermal.