Dr. Energy Saver’s Whole House Fan Cover is installed over your fan assembly and sealed airtight with expanding foam. It stops air leakage and insulates over the fan. Made of lightweight, high-tech SilverGlo foam insulation, it also has a radiant barrier (foil) on the flat top to reflect heat back in during winter and out in the summer, so the insulation isn’t doing all the work by itself. This cover is completely compatible with our TruSoft blown insulation in your attic.