5mm (1/4 inch) closed cell polyethylene foam sandwiched between pure aluminum on both sides.Heating and cooling costs are about 60% of the average American Household energy bill. The most effective way to cut these cost is to lower the amount of heat transferred into the home in the summer an out of the home in the winter.Our Radiant Barrier/Reflective Insulation is made from double-sided 99% aluminum foil, with closed-cell polyethylene foam. Additional Details ------------------------------ Product description: 5mm (1/4 inch) closed cell polyethylene foam sandwiched between pure aluminum on both sides.Heating and cooling costs are about 60% of the average American Household energy bill. The most effective way to cut these cost is to lower the amount of heat transferred into the home in the summer an out of the home in the winter.Our Radiant Barrier/Reflective Insulation is made from double-sided 99% aluminum foil, with closed-cell polyethylene foam.