Insulate your new or existing 8 in. duct pipe with this Master Flow 8 in. Dia Fiberglass Insulation Ductwork Sleeve. Enjoy consistent air temperature and reduced system condensation and noise. On new pipe installation - simply slide the sleeve over the 8 in. duct pipe as it is being installed. For existing duct pipe up to 8 in. Dia cut the jacket length wise (insulation is pre-cut) and wrap around the pipe.