Master Flow Water Based Air Duct Sealant helps seal all types of air ducts to reduce the risk of conditioned air leakage. Sealing air duct plenums, takeoffs, elbows, and vent boots where they connect and sealing the seams, per product instructions, may help save energy. The sealant is fiber reinforced and easy to apply by brush, gloved hand, or putty knife to flex duct, duct board, and sheet metal air ducts. It dries to a tough, flexible, and weather resistant seal. It adheres to many surfaces like: drywall, foam and fiberglass insulation, galvanized steel, aluminum, masonry, and wood. This product is also available in 1/2 Gal. tub.