Dundas Jafine BPC425R6 Insulated Flexible Duct with Black Jacket, 4-Inches by 25-Feet 4" x 25' Length R6 Insulation value. Required minimum in many building codes across the country Polyethylene jackets provide a durable, scuff-resistant vapor barrier that provides improved protection against damaging ultra-violet light. Installation is made easy with the reinforcing fiberglass yarn scrim, which acts as a rip-stop and prevents tearing Rigorously tested by Underwriters Laboratories, Inc. in accordance with UL 181, The Standard for safety in Factory-Made Air Ducts and Air Connectors.