This disclosure relates to a method of filtering air for use in a combustion engine. A filter is utilized that comprises a treated filter fabric and a treated filter foam. The treated filter fabric and the treated filter foam include an ionizing agent, a binder comprising guar gum and ammonium sulfate, and an organo silane quarternary amine antimicrobial. Air is directed into the treated filter fabric. As air moves through the treated filter fabric, a first set of contaminants is removed. The air is then directed into the treated filter foam, which is positioned adjacent to the treated filter fabric. As the air moves through the treated filter foam, a second set of contaminants is removed.