Air filter with expandable filter media

An air filter assembly comprises a plastic frame containing an air permeable filter media. The media is corrugated to provide a series of pleats. Some of the pleats can be folded more compactly than others, so that the media can fit in various size frames. This can reduce the inventory of filter manufacturers and dealers. The filter frame can be plastic injection molded with integral living hinges to enable the frame to fold from a relatively flat shape to a more box-like structure. The frame includes one or more flip-up saw tooth racks that help define a main series of chambers plus a storage chamber. The main series of chambers supports a portion of the media that is more loosely folded for filtering air. The storage chamber is adjacent the main air stream and holds the more compactly folded, excess pleats.