Insulate your new or existing 6 in. duct pipe with this Master Flow 6 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 6 in. duct pipe as it is being installed. For existing duct pipe up to 6 in. in diameter - cut the jacket length wise (insulation is pre-cut) and wrap around the pipe.