Abstract: An air filter for filtering particulate matter from air flowing therethrough to a point of use requiring clean air, includes an imperforate front wall, a perforate back wall and opposite, imperforate side walls. The front wall is smaller in height than the back wall and a pair of pleated filter elements extend from the top of the front wall to the top of the back wall and from the bottom of the front wall to the bottom of the back wall, respectively, defining a wedge-shaped outlet space between the filter elements extending from the front wall to the back wall and being larger toward the back wall. A plurality of the filters are adapted to be stacked one on top of the other to define a plurality of inlet spaces therebetween and a plurality of outlet spaces. Reinforcing members are interposed between the filter elements in each filter, whereby the filter is enabled to support the weight of a man thereon.