Open cell polyurethane foam is designed especially for filtration in critical environments. A photo enlargement of the foam filter media shows a uniform network of connected strands that form a maze that dirty air can't avoid. The foam inner filter is coated with sticky oil. Air is pulled through the entire volume of the foam element, (not just the surface) and dirt particles are thrown into contact with the sticky strands. High airflow and filtering efficiencies are achieved. The addition of a dry outer wrap helps to knock larger dust particles away from the inner wet filter. UNI 2-Stage Foam Air Filters are available in many popular sizes to fit Weber and Dellorto carburetors.