Johns Manville's Spiracoustic Plus® is a spiral duct liner system engineered to provide superior acoustical and thermal performance for spiral air duct interiors with an airstream diameter of 6 inches and larger. Spiracoustic Plus delivers significantly improved acoustical and thermal performance compared to double-wall construction, all at a competitive cost for the system. It is manufactured with evenly-spaced kerfs to allow the material to conform to the inside diameter of spiral ducts, producing a finished airstream surface. This surface is coated with our proprietary Permacote® coating, which provides a durable surface and added product protection against microbial growth. As an added benefit, the exterior surface is laminated with a tough fire-resistant FSK facing.