Trapped particles can restrict airflow, and if dirt works its way into your engine, a pinhead-sized granule will gouge your cylinder, piston and rings like a bullet. The course, open-pore outer foam catches airborne dirt, grime and sand while a fine, open-pore inner foam acts as a second filter to trap small particles ensuring maximum air passage. Twin Air's Standard air filters feature an exclusively formulated adhesive that withstands repeated cleanings and a greaseless foam sealing ring that acts as a breathable gasket for increased air passage. Pre-Oiled filters are treated with Twin Air® BIO Foam Filter Oil using state of the art filter oiling machines, which provide the ultimate consistency in pore coverage. The same treatment that Factory Race Teams and O.E.M.s receive is now available to all Twin Air customers.