These are the multifoil materials which include foil backed bubble wrap.
Foil backed bubble wrap insulation.
Most metallic bubble wraps are about an r 1.
I have heard some say that the insulation could be installed loosely to maintain the gap.
Foil faced bubble wrap is composed of either one single bubble or two double bubble layers of mylar air bubbles sandwiched between two metalized surfaces.
Double bubble reflective foil insulation 24 inch x 10 ft roll industrial strength commercial grade no tear radiant barrier wrap for weatherproofing attics windows garages rv s ducts more.
This effectively acts like a mirror reflecting heat back to where it came from.
Some insulation materials don t work 100 on trapped air.
Worth mentioning to get the equivalent r value to what the manufactures claim on the packaging the installer has to use spacers under the insulation to keep the prescribed air gap between the ducts and the foil.
Double bubble reflective foil insulation 24 inch x 10 ft roll industrial strength commercial grade no tear radiant barrier wrap for weatherproofing attics windows garages rv s ducts more.