RCD Corporation® #6 Mastic® low to high velocity air duct sealant is preferred by professional HVAC and home weatherization contractors nation wide for permanently sealing the joints and seams of thermal insulation, crawl space vapor retarder, house wrap and all air duct types including UL listed air ducts. #6 Mastic® seals leaks in return air ducts, supply ducts, air handlers, plenums, grilles, registers, dampers, and boots and is used in home sealing  to reduce air infiltration into the living area. Sealing the home from air infiltration, sealing air ducts and crawl space sealing improves indoor air quality, reduces humidity, increases comfort and saves energy. Easy application by brush, trowel, palm, spray, or extrusion. As seen in Money Magazines 35th Anniversary Issue October 2007, Discovery Channel's show: Dirty Jobs season 4 episode 13,  and Bob Vila's Home Again show #606.