The Hi-E 40I is a medium efficiency pleated filter specially constructed for use in systems requiring UL Class I listed products. The perimeter frame is constructed of UL approved non-flammable board. The pleated media is bonded upstream and downstream to diagonal support elements to increase filter stability. The media is a special 1/8' thick, high density, ultra-fine fiberglass reinforced by a woven fiberglass mesh. The hi-E 40I offers 30-35% average efficiency and 90-93% average arrestance when tested in accordance with ASHRAE 52.1-1992.