Uni Filter Two Stage Competition Air Filter - NU-1418ST Will NOT Void Vehicle Warranty. Works with Original Equipment Manufacturer Vehicle Electronics. Uni Foam Air Filters use polyurethane foam as the filtration media because of it's superior dirt capturing abilities. "Open Cell" Polyurethane Foam is wetted with specially developed filter oil. The "sticky" filter oil is suspended in the path of the dirty air making it impossible for dirt to pass through the depth of the filter.