Airaid premium filters consist of multiple layers of cotton gauze plus one layer of synthetic fiber material called SynthaFlow, sandwiched between either stainless steel or aluminum mesh, depending upon the application. The casing of the filter is hand-poured urethane, which offers superior performance and durability, and won't shrink or crack from prolonged heat exposure under the hood. Superior filtration and flow, thanks to the SynthaFlow material, is what makes Airaid premium filters better than the rest. SynthaFlow enhances dirt filtration down to two microns and is moisture repellent. Airaid premium filters are also washable and reusable and are guaranteed for life.