Electrostatic air filters, also known as washable filters or reusable filters, are located on a furnace and typically take the place of a pleated filter. The main purpose of any filter is to clean the dirty, outside air that is being forced into your home. \n \nOur metal frame filters are made from a single piece of roll-formed galvanized steel fastened together at one corner with a single rivet. Metal frame filters are available in 1″ depths. They have 2 layers of polypropylene between 2 layers of expanded steel for improved air flow and rigidity with white polyester ultra-high loft impingement filtering center layer.