Polyken/Nashua 360-17 FoilMastic Butyl Rubber Tape is a printed, 2 mil dead-soft aluminum foil backing with a 15 mil butyl rubber mastic adhesive. Used for indoor or outdoor sealing of low, medium & high pressure HVAC duct systems (includes: metal duct, fiberglass duct and flexible duct systems). Seal cracks and seams in gutters, roof alleys, eaves, hips and ridges. Seal around chimneys and vent stacks. Repair gouges, rips, tears in metal panels of trailers, shipping containers and metal buildings. Also used to seal leaks in vans, cars, and trucks and for mobile home repair. Use duct mastic to mend poorly sealed connections; improve indoor air quality (since fewer pollutants circulating); lower utility bills; and burn fewer fossil fuels. SMACNA A, B, and C Seal Classes. UL 723 classified. Features include: Permanent sealant. Provides instant water tight bond. Acceptable for use on galvanized materials. Heavy duty all weather foil coated butyl mastic. Excellent adhesion to all surfaces. Extremely conformable. Non-staining adhesives. Paintable 2mil foil backing (use in place of caulk). Excellent resistance to cold, heat, water, and sunlight. Printed for easy identification. Release liner provides ease of installation. NOTES: Sizes shipped will often be to the tape-industry standard metric equivalent, i.e. 24mm for each 1 inch of tape width. This product's actual size is 48mm x 30.5m.