An air filter is a device which removes contaminants, often solid particulates such as dust, pollen, mold, and bacteria from air.
They are often used in internal combustion engines, gas compressors, diving air compressors, ventilation systems and any other application where air quality is important. The air intakes of internal combustion engines and compressors tend to use either paper, foam, or cotton filters. Oil bath filters used to be common, but have fallen out of favor.
Some buildings, as well as aircraft and other man-made environments (e.g., satellites and space shuttles) use foam, pleated paper, or spun fiberglass filter elements. Another method uses fibers or elements with a static electric charge, which attract dust particle.