If you have cast-iron radiators, you can DIY a heat reflector out of aluminum foil. Tape some heavy-duty aluminum foil to a piece of cardboard with the shiny side up. That’s literally it.
Metal foils and foil stock are very thin, metal-mill products with a thickness that is usually less than 0.006 in. Copper foil and aluminum foil are the most common types of metal foils and foil stock ...