Water-based fiber-reinforced duct sealant/mastic formulated for indoor/outdoor use. Meets U.L. Class 1 rating and local codes while featuring long term flexibility and strength. Use on metal heating, ventilating and A/C duct systems, as well as fiberglass duct board systems and flex duct systems. Recommended for use to 10 in. Of water column pressure without the need for fiberglass mesh reinforcement.