Butyl gasket is used in tape and bead form to seal transverse duct connections systems helping to provide a moisture and air tight seal. This tighter seal also helps reduce energy waste and noise. Wherever flanges are used in connecting parts of a duct system, the potential for air leakage exists. Besides contributing to energy waste, leaks can also create noise. Sealing of ductwork can be accomplished with the use of a pliable material which adheres to flanged surfaces. When this material is attached to a flange which is then assembled to a second flange, the material is compressed and fills gaps and irregularities creating a flexible seal. Duro Dyne BTL500 is a UL Classified permanently soft caulking compound designed for sealing flanged joints in duct systems. It adheres to clean dry metal surfaces and does not promote corrosion.