Insulated flexible ductwork is used to connect bathroom exhaust vans to the exterior vents. It also can be used for air conditioning ductwork as well. Because the insulation can irritate the skin, it's wise to wear work gloves when installing this type of ductwork.
When attaching the ductwork to the neck of the vent, at least two layers of HVAC metal foil tape are necessary to prevent any leakage, and smoothing out wrinkles ensures that the seal is airtight. A similar seal connecting the ductwork to the exhaust fan in the bathroom keeps the humidity in the bathroom from causing mold or other issues in the attic.