Just as sunglasses absorb the harsher parts of sunlight, many materials absorb the longer infrared (IR) wavelengths that are invisible to the human eye. Some IR-absorbing materials you see every day include window glass, plastics, metals and wood. Your skin also absorbs IR, allowing you to feel the warmth of sunshine or a bonfire. IR-absorbing materials have many uses, such as trapping heat, such as the glass of a greenhouse, or blocking it, like the metal walls of a furnace.
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Common infrared-absorbing materials include windows, plastics, metals and wood.
Materials that Absorb IR Wavelengths
Most materials absorb some IR wavelengths although it may be only a small percent. Others, such as water vapor in the Earth’s atmosphere absorbs the majority of the IR radiation that comes from the sun. In addition, carbon dioxide, ozone and oxygen also absorb much of the IR radiation, allowing very little to actually reach the ground. Aside from water vapor, bodies of water on the surface of the Earth also absorb IR wavelengths well. Glass, Plexiglas, wood, brick, stone, asphalt and paper all absorb IR radiation. While regular silver-backed mirrors reflect visible light waves, allowing you to see your reflection, they absorb infrared radiation. Gold, manganese and copper also absorb IR radiation well. According to Next Energy News, the U.S. Department of Energy is using these three metals to design nanoantennas, which will convert waste heat in the form of IR radiation into electricity.
Materials that Reflect IR Radiation
Aluminum foil is a strong IR reflector. Placing sheets of aluminum foil behind your radiator on an exterior wall can reduce heat loss through the wall. Snow’s ability to reflect IR radiation back into space helps to keep the planet cooler. If your car sits in the sun too long, it becomes too warm inside. Partly this is from trapping visible light waves, but a bigger effect is the absorption of IR radiation by the car’s paint.
Materials that Radiate IR Radiation
Almost everything in the universe radiates IR wavelengths unless it is at minus 273 Celsius (minus 460 degrees Fahrenheit), which is absolute zero and is the coldest possible temperature. At this temperature, the bonds in a molecule stop rotating and it has no more energy to radiate as heat. Interestingly, materials that are good at absorbing infrared radiation are also good at emitting, or radiating, that radiation. Even glaciers emit IR radiation although at much lower levels than water. Incandescent light bulbs emit a lot of IR radiation along with visible light, whereas the newer fluorescent bulbs do not.
Object Color and IR Absorption
Darker colors absorb the visible wavelengths in sunlight, not IR rays. Therefore, the color of the material is unimportant in the ability of a material to absorb infrared light. That may change, however, with the development of new technologies. According to Plastemart, new pigments designed to reflect IR radiation will soon keep the car interior cooler.