3M Heavy Duty Duct Tape 3939 is composed of a waterproof polyethylene film over cloth scrim backing with a rubber adhesive used for demanding duct tape applications. Conformable and moisture resistant backing that tears easily by hand. Tested according to UL 723 and ASTM E84. Transportation, aerospace, automotive, commercial vehicle, RV, bus, truck, ship yards, military, metal working, furniture, electronics, solar, trailer manufacturing and woodworking. Sealing, holding, bundling, reinforcing, identifying, tabbing, wrapping, splicing and protecting.