339 is a UL 181A-P & UL 181B-FX Listed cold weather foil tape. High performance acrylic adhesive Excellent cold weather performance and performs in hot, humid weather as well. Suitable for installation temperatures as low as -10F. Applications: Recommended for use on rigid fiberglass duct board and rigid sheet metal duct in accordance with manufacturer instructions. Class 1 flexible duct sealing. Insulation seam and patch. Dryer vent seals.