Flanders Pre-Pleat 40 LPD achieves the highest dust holding capacity and the lowest pressure drop in the industry. These filters are UL 900 classified. 100 percent synthetic non-woven, proprietary media that can be recycled. Newly designed expanded metal is continuosly laminated on the air leaving side to provide pleat stability while eliminating flutter during operation. Heavy duty, two piece, moisture-resistant frame includes diagonal and horizontal support members bonded to the media on the air entering and exiting sides for unsurpassed frame strength.