Insulated Ducting is made with wire reinforcement, keeping the duct in shape no matter where it’s installed. Sandwich ducting has this wire added while the duct itself is being fabricated. This puts the wire within the four layer seams, and can still have wear stripping added for extra protection. Duct-in-Duct is made with a standard wire reinforced duct on the inside, and doesn’t need additional wire on the outside.