the filter of the present invention continually provides the passenger compartment of a vehicle with a supply of purified air , even in the most severe environmental conditions . the filter comprises an inlet surface , an outlet surface , walls which define a plurality of passages which extend from the inlet surface to the outlet surface , and a filtration means for removing the impurities from the fluid . the filter preferably can be subdivided into a plurality of layers , including an inlet layer , an intermediate layer , an outlet layer . each layer includes a plurality of cells , the cells having walls with a generally curvilinear shape . a plurality of the passages are preferably in fluid communication with a plurality of other passages . surface filtration is used to remove the impurities from the fluid flowing through the passages . the impurities are retained within the filtration means which are disposed on the walls , as the fluid flows through the passages essentially unrestricted even when the removing means is saturated with impurities .