Abstract: An air filter assembly including a molded rectangular frame. The frame includes a filter element supporting and backing portion and an integral peripheral flange portion. The filter element supporting and backing portion is generally planar and is formed with a multitude of discrete circular apertures arranged in a pattern to permit air flow therethrough. The flange portion has a channel shaped cross section defined by inner, outer and connecting walls. The inner and outer walls slope towards each other to permit one rectangular frame to be nested inside another. The outer wall of the flange is shorter than the inner wall and legs are formed as part of the outer wall with the legs being longer than the outer wall but somewhat shorter than the inner wall. The frame is preferably molded from reprocessed paper pulp. The frame is bowed a slight amount longitudinally in the direction of normal air flow through the filter element.