Bel-Ray, foam air filter oil. 1 liter bottleOil for foam air filters. For all street; off road; and racing foam air filter applications. It is easy to apply and improves airflow. The ultra viscous formula forms an oil barrier to trap micron sized particles. It is waterproof and prevents clogging when wet. Designed to improve air flow Traps microscopic particles to extend engine life Waterproof formula prevents clogging when wet.