This 4 inch (10.2cm) flexible duct tubing is insulated and UL listed. It is intended for use with the Ceiling Vent System (VS-CVS). This tubing will connect to the exhaust end of rough-in box and carry the heated air inside the walls or ceiling to vent to another area in the home. Optimally, this will connect to the HVAC return system allowing the heated air to mix with the air in the home and then be recycled by the HVAC system. When using ducting, ensure to use a high quality HVAC sealing tape (not duct tape) to ensure there is no air leakage.