Abstract: A composite filter media for bag or pocket filters and the like includes an upstream dirt-holding layer of fine polymeric fibers and a downstream high efficiency filtration layer of glass fibers. The upstream layer includes polymeric microfibers having a mean fiber diameter ranging from about 2.5 to about 4.5 microns, lofting fibers and binder fibers; and weighs between about 2.0 and about 7.0 grams per square foot. The glass fiber layer has a weight between about 1.2 and about 2.7 grams per square foot; the average diameter of the fibers in the glass fiber layer is within a range from 3.0.times.10.sup.-5 to 4.1.times.10.sup.-5 inches; and the fibers are bonded together at their points of intersection with a binder. The composite filter media has an average air filtration efficiency of at least 80%.

Abstract: An air filtration media is formed of a blanket of fibers, preferably glass fibers, bonded together at their points of intersection with a binder. The blanket has a weight between about 2.5 and about 4.0 grams per square foot and the average diameter of the fibers in the blanket is within a range from 3.0 .times.10.sup.-5 to 4.1.times.10.sup.-5 inches. The blanket has an average air filtration efficiency of at least 80% and the pressure drop across the thickness of the blanket is no greater than 0.30 inches of water. The blanket can be used alone; with a permeable backing sheet; or with a second layer or blanket of filtration media, as part of a dual-phase or multi-phase air filtration media.

Abstract: Air filtration media is formed by collecting a layer of fine diameter glass fibers directly on a foraminous, reinforcing, backing layer and subsequently collecting a layer of relatively coarse diameter glass fibers directly on the layer of fine diameter glass fibers. A bonding agent carried by the glass fibers is then cured to bond the glass fibers within each layer together at their points of intersection, to bond the layers of fine and coarse glass fibers together and to bond the layer of fine diameter fibers to the backing layer. This method of forming the composite air filtration media permits the particle efficiency and the dirt loading capacity of the composite air filtration media to be adjusted during the production of the media by adjusting the diameters of the glass fibers in one or both of the layers and/or by adjusting the density of one or both of the layers.