Speedi-Products FD-25R8 04 4-Inch Diameter by 25-Feet Length R8 Insulated Flexible Duct with Metalized Jacket R8 fiberglass insulation for improved energy efficiency & noise absorption Polyethylene sleeve separates airflow from insulation Cut to length for each specific application Can be used in Supply, Return and standard exhaust applications Not for use in Kitchen Hood Exhaust systems