I use spray cleaner, like brake kleen, I spray out the foam and it gets real "puffy" from the brake cleaner. Gets like twice it's size. Then I blow it out with compressed air. Once it dries it's back to it's original size. I reoil it with K&N filter oil and good to go. Soap and warm water is the safest though. Just be sure it's thoroughly dry and reoiled before running.