This is a standard grade disposable furnace filter of the same type that has been protecting furnaces and central air conditioners around the world for over 50 years. The filtering medium is continuous filament spun glass. The frame is made with one continuous piece of chipboard to guard against corner separation. The EZ Flow II has no media retainer - Instead, the media is adhered directly to the frame for non-metallic applications. For peak equipment protection and energy efficiency, these filters should be changed monthly in periods of high use.