I have been using cotton sheets from Goodwill as a reflective surface for years.You can even put a layer of flat white paint to make a brighter surface.Theres no problem with heat.I hang each sheet( 2-3) over rods.I then tuck the sheets in at the bottom and pin them together on the sides.I blow the fan in one side and the sheets balloon to make a highly refective bubble around the plants.You can see the reflected light on the shade side of the buds.-usdi Agaluga