Airaid materials are the highest quality available. Most washable filters use only three or four layers of oiled cotton gauze. We utilize five layers to assure the cleanest air possible. The fifth and "last layer of defense" is a synthetic media. This produces the cleanest air if any washable filter! Increase your airflow and maintain maximum filtration. AirAid's "four + one" filter construction out-performs the others in clean air testing. Our competitors' airflow gains come at the expense of inferior filtration. AirAid provides the optimum balance between maximum airflow and maximum filtration.