IDEAL 5 lb. duct seal in dark gray putty color is ideal for sealing metal, masonry, wood or plastic. It offers 1.65 specific gravity and is non-toxic. It has calcium carbonate, magnesium aluminum silicate, crystalline quartz silica, butane polymer, synthetic polymer, carbon black, antioxidant, cellulose fiber, aluminum silicate, tall oil rosin and naphthenic wax composition. Duct seal is UL listed.