The K/N Filters Airforce Foam Pre-Cleaner Air Filter extends service intervals of standard K/N Filters in particularly dusty conditions.The Airforce Foam operates by reducing the larger particles transferred to the main filter, stopping up to 90% of dust yet only restricting air flow by 2%. Developed for particularly dusty environments, the Airforce filters provide extra insurance against unwanted airborne particles entering the intake system. The Airforce filters are designed to be cleaned with K/N Cleaner or soap and water.Red coloured Airforce pre-cleaners need to be oiled with K&N air filter oil after they have been cleaned. Gray coloured Airforce pre-cleaners do not require oiling as they have smaller foam cells.