DetailsNon-insulated UL181 Class 1 flexible air duct, extremely strong with heavy fiberglass cloth fabric permanently bonded to a corrosion resistant spring steel wire helix. For all pressure heating and cooling systems. A superior alternative in applications where insulated duct is not required or cannot be used, e.g., clean room applications. Unlike connector-rated products, S-TL is not limited to length of run. Bag.