Seal all of the joints along the duct run with UL 181-approved foil duct tape. Wrap around the duct a few times to create a strong air seal.
Secure one end of the duct wrap insulation roll around the duct where it meets the fan housing, using the duct tape (or other tape recommended by the manufacturer).
Wrap the duct in a continuous spiral fashion, overlapping the edges of the insulation by at least 1 inch (or as directed). Note: Some duct wrap products are installed by wrapping cut lengths of insulation perpendicularly to the duct, and taping each section together with duct tape.
Other types of insulation require spacers to create an air gap between the duct and insulation. If you’re using fiberglass insulation, be careful not to pull and stretch the wrap; compressing the insulation compromises its effectiveness.
Complete the duct wrapping up to and around the collar of the vent cap at the exhaust end of the run. Seal the insulation to the vent cap with the duct tape.