Duct-Seal 321 Grey, 1 Gallon Pail, Is An All Purpose Industrial Grade Duct Sealant For All Types of Metal Duct, Glass Fiber Duct Board, and Flex Duct, As Well As Duct Fabric and Flexible Tubing Runouts. It Includes UV Inhibitors For Extended Outdoor Exposure and Built-In Fiber Reinforcement For Added Strength. This Non-Toxic Water Based Product Is Solvent Free and Is Suitable For Residential Use.