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 US ENERGY PRODUCTS is made from double-sided 99% aluminum foil, with closed-cell polyethylene foam. It provides optimal protection by reflecting up to 97% of radiant energy, in addition to resisting conductive and convective heat transfers. Our Radiant Barrier/Reflective Insulation US ENERGY PRODUCTS is nontoxic and non-carcinogenic and works ideal for hot and cold climates.