Bel-Ray Foam Filter Oil. For case order quantity 12. Bel-Ray Foam Filter Oil is for all street, off-road and racing foam air filter applications. Innovative Bel-Ray technology has produced a foam filter oil unlike any other. It is easy to apply and improves airflow. Ultra-viscous formula forms an oil barrier to trap micron-sized particles that can cause engine damage. Waterproof formula prevents clogging when wet.