The All-Filters Flat Panel Disposable Polyester Air Filter is a standard grade 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 nonwoven polyester media. Filter frames are made of beverage board, which stays strong through humidity and temperatures up to 200° F. For peak equipment protection and energy efficiency, these filters should be changed monthly in periods of high use. This filter is effective against the following contaminants: household dust, as well as debris and lint. Lasts up to 30 days. UL Class II rated. Protects heating and air conditioning equipment. Sturdy chipboard frame and metal retainer contributes to filter strength.