Having an air filter in car engines is very important. Its presence provides a form of respiratory system for your car engine – it screens the air of dust and other impurities in the air before it mixes with the fuel for combustion in the engine. The air filter prevents these unwanted foreign particles from entering and possibly causing damage to the engine.
Usually the air filter in car engines is a form of a particulate air filter, in which fibrous materials such as paper (not the usual paper), cotton or even foam. The pleated paper filter is the usual choice for an air filter in car engine cleaners, because of its efficiency, easy maintenance and affordability. The filter is not actually made of the usual paper for writing but is a specialized paper-like fibrous medium. If sized appropriately to a certain engine, the pleated paper filter works well and becomes only restrictive to flow when it is really clogged with particulates (contrary to the belief popular amongst car tuners that a paper filter does not allow good flow of air and thus diminishing engine performance).
The air filter in car engines is usually oiled to facilitate air flow into the engine. The filter and its holder are housed in a plastic or metal box, connected to the intake manifold via a large-diameter tubing which allows air to flow into the filter and ultimately to the engine. And for the exhaust, a chemical filter, known as the catalytic converter, is also present to minimize the pollution produced with the burning of fuel.