The IRD-3DE Access Door is to be installed on an outside insulated rectangular ducts. The insulation is soft and covered with an aluminum foil. Can also be installed on double-wall ducts.
Take the self-adhesive paper template and apply onto the duct making sure it is well centered inside the opening you just created in the insulation. Then cut the duct along the edge of the template.
Then install the access door by inserting its inner cover at an angle inside the duct. Turn it straight and pull slightly to align it with the opening.