Do Car Sun Shades Really Work? What the Science Says

Car sun shades are cheap and simple, but do they do anything? Motor1 says they do, although the benefits are not quite what some ads suggest.

A parked car heats up because sunlight passes through the windows and is absorbed by the dashboard, seats and steering wheel. Those surfaces warm up and heat the air around them. A windshield shade interrupts that. Reflective ones bounce some of the sunlight back out through the glass, and dark or opaque ones block direct light from reaching the area they cover.

The effect can be measured. Researchers at the Florida Solar Energy Center found that a plain cardboard windshield shade lowered the average air temperature inside the car by about 15 degrees Fahrenheit (8 degrees Celsius) on sunny days. Dashboard temperatures dropped by about 40 degrees Fahrenheit (22 degrees Celsius). Results depend on the car, the outdoor temperature, how strong the sun is, the design of the shade and how long the car is parked. A shade will not stop all heat, and the inside of the car can still get dangerously hot.

Using one correctly matters:

• Put the reflective side toward the windshield, following the maker's instructions. - Cover as much of the glass as you can, without big gaps around the edges. - Hold it in place with the sun visors or its built-in attachments. - Use it whenever you park in direct sun, even for a short time. - Think about side-window shades for passengers, especially children, but never use them where they block the driver's view while driving. - Store it neatly when you are not using it.

A shade that fits well is usually more useful than an expensive one that leaves large gaps. Using it every time you park in the sun works better than remembering only on the hottest days. Basic cardboard or fabric shades can block direct sunlight, and reflective shades are designed to reject more of the sun's energy. Some have several layers or insulating materials.