Muffler-Duct is a fully flexible, thermally insulated ducting that is specially designed for the HVAC market. Muffler-Duct is composed of three layers that work together to stand up to the most demanding applications. The inside is made of Al-Foil duct, in the middle there is a flame retardant pearl wool, then we use a white reinforced PVC sleeve with an encapsulated high tensile steel wire helix. Engineered for heavy flow, Muffler-Duct reduces noise and condensation. Over-sized to fit easily onto connections. Available in sizes 4″ – 14,” 25 foot lengths, 2 clamps included.