What Materials Reflect Infrared Light?
Gold, silver, aluminum, Plexiglas and hybrid pigments are materials that reflect infrared light. The atomic makeup of materials is what renders them transparent, opaque or reflective to infrared radiation.
Infrared radiation occupies the part of the electromagnetic spectrum that is just below visible light, and it has a wavelength ranging from 0.7 to 300 micrometers. Gold beaten into very thin sheets is good at reflecting the lower end of the visible range of the spectrum, which includes red and yellow light. This reflectivity also extends into the infrared range, making gold foil an ideal material for high-performance heat shields. Many components used in spaceflight are coated in gold foil for this reason. Gold also blocks other parts of the electromagnetic spectrum, including ultraviolet radiation, which has a wavelength shorter than the shortest visible light. This ability to selectively filter out radiation on both sides of the visible spectrum enables gold as a visor material for astronaut helmets.
Aluminum also reflects infrared radiation, although thin sheets of it are not as transparent in the visible light range as gold. However, aluminum is much more abundant than gold, making it ideal for conventional infrared radiation-shielding applications. Using aluminum foil to bake goods in an oven shows the ability of this material to internally reflect infrared radiation and trap heat.