US Patent 7150774 Self-spacing pleated filter insert

A replaceable, self-spacing, pleated, filter insert that can be easily installed in a reusable filter frame without the aid of a secondary spacing structure includes reversibly collapsible and expandable filter media including a plurality of pleats that expand uniformly when the filter is expanded. When the filter is expanded to the length of the filter frame, the filter is under tension and behaves like a spring, thereby allowing the length of the filter to be readily adjusted to match the length of the frame and allowing the pleats to be aligned with corresponding ribs provided in the frame.