Abstract: Sandwich unit for a heat insulating wall coating having a surface layer facing the room confined by the wall, an intermediate layer adhered to the surface layer and being of plastic foam, and a third layer adhered to the intermediate layer and facing the wall. The third layer comprises an electrically insulating plastic foil and metal flakes embedded in the plastic foil and thereby electrically insulated from each other. The flakes are disposed with their broad side parallel to the foil and overlap each other to form an unbroken total surface for reflecting heat radiation.