Insulating a room in the summertime with aluminum foil can help keep sunlight out of the room and lower temperatures. Completely cover all windows with aluminum foil and secure it with a heavy-duty tape such as duct tape. The shiny surface will reflect the sunlight's rays. You can also insulate cold food when it will be near the sun.
Because aluminum foil reflects light, it can be used for insulation, especially in areas that need to be guarded against heat. When it is used with other materials, it can be used to warm an area, too. Other materials such as paper and cotton, do not have the reflectivity that aluminum foil does, so when the sun is bearing down, they will not keep it out as well. An area that is already hot will be kept hot by aluminum foil, as it will hold in hot air. Paper and cotton will release heat at a quicker rate than aluminum foil. Aluminum foil can keep things like wires or pipes insulated, as it traps air when it is wrapped around an object. This can be achieved with several objects, though, and not just aluminum foil.