However, this kind of air filter has low filtration efficiency, heavy weight, high cost and inconvenient maintenance, and has been gradually eliminated in automobile engines. The filter element of the paper dry air filter is made of resin-treated microporous filter paper. The filter paper is porous, loose, folded, has a certain mechanical strength and water resistance, and has the advantages of high filtration efficiency, simple structure, light weight and low cost. It is the most widely used air filter for automobiles with the advantages of low cost and convenient maintenance. Polyurethane filter element The filter element of the air filter is made of soft, porous, sponge-like polyurethane with strong adsorption capacity. This air filter has the advantages of a paper dry air filter, but has low mechanical strength and is used in car engines. more widely used. The disadvantage of the latter two types of air filters is that they have a shorter lifespan and are unreliable in harsh environmental conditions.