48-81 Eco-Duct® Seal is a tough, flexible water based duct sealant specially formulated to meet the requirements of UL 181A-M & UL181B-M. The sealant is for use on Fiberglass Ductboard, Flexible air ducts or Air connectors and metal duct systems. The product can be used for sealing low, medium and high-pressure heating and air conditioning ductwork. 48-81 Eco-Duct® Seal is suitable for outdoor use. 48-81 Eco-Duct® Seal is fiber reinforced.