Sound Seal Acoustical Pipe and Duct Lagging Flexible Noise Barrier: B-20 Lag / QFA-9 is typically used to wrap noisy pipes and ducts to block the noise that transmits through the walls of the pipe or duct as air or other contents move through it. The quilted fiberglass decoupler also provides sound absorption and thermal insulation around the pipe or ductwork. The two-pound per sq. foot barrier and the two-inch thick quilted fiberglass absorber improves overall acoustical performance, especially at low frequencies. The reinforced-foil exterior readily accepts a matching lag tape for easy installation and also serves as a protective jacket for indoor or outdoor applications.