AIR-TIGHT™ FDS-181 DUCT SEALANT is a fire-resistive, fibrated, water-based sealant for indoor or outdoor low, medium and high velocity heating and air conditioning ducts. It performs as a tough and flexible adhesive and sealant, forming a durable seal against air leakage on faced duct board, flex duct and galvanized, aluminum and stainless steel metal ducts. Mechanical fasteners of the type and number normally used for duct assemblies are required to provide rigidity to the duct system.