Foster 32-19 Duct-Fas Duct Sealant is a fire resistive, water based, indoor/outdoor, U.V. resistant, non-fibrated sealant for use on high velocity ducts to form a flexible yet durable seal against air leakage. Foster Duct-Fas Duct Sealant has been specially formulated for ease of application, clean “break-off”, and nonslumping at elevated temperatures.