Double Bubble Foil Reflective Insulation, 48-In.48" x 50', standard edge double bubble foil both sides reflective insulation, 5 16" thick with two outer layers of aluminum foil, each foil layer is bonded to a tough layer of polyethylene for strength, reflects up to 97% of radiant heat, r value up to 14. 3 depending upon application, excellent vapor barrier for below grade, can be used for crawl space, duct insulation, side walls, metal buildings, basement walls & attics, product has been evaluated