This Imperial Duct Insulation Sleeve works as an energy-efficient insulation blanket suitable for heating, ventilation, and air conditioning systems. Specifically designed to insulate rigid or semi-rigid round ducts, it is an excellent method for reducing heat or cool loss and condensation build-up. The sleeve is made of a thick fiberglass insulation blanket enclosed in a strong, fiberglass-reinforced silver metalized outer jacket. The insulation sleeve measures 4-in x 25-ft, meets UL 181 standards for Class 1 Air Duct, and features an energy-efficient insulation R-value of 6.0. Check your local building codes prior to installation.