Duct sealing with mastic, Metal-backed tape, Or aerosol sealant.

* Mastic is gooey, but highly effective adhesive for sealing duct connections and dries to a soft solid.
( UL 181 Approved )

* Foil tape has metal foil backing and acrylic adhesive.
( UL 181 Approved )

* Aerosol sealent is a sticky vinyl polymer ( Needs to be professionally installed )