Abstract: A heat reflector for temporarily covering of a window or a door to reflect sunlight and reduce heat transfer therethrough includes a metallized, biaxially-oriented polyethylene terephthalate sheet. The heat reflector can be sold in kit form comprising the sheet of metallized polyethylene foil; a cutting element for cutting the sheet of metallized polyethylene foil to fit the window or door; a mounting element for temporarily mounting the polyethylene foil layer onto a window or door; and a squeegee for smoothing out the metallized polyethylene foil on the window or door.