A filter 1 used in an exhaust system for an engine comprises a base material having a plurality of cells 4 forming gas flow paths and having a gas inflow-side end portion 2 and outflow-side end portion 3, and a plurality of porous partition walls 5 defining the cells, the end portions of at least some of the cells being closed off (i.e. wall-flow filter). The void occupancy of a catalytic substance within pores of the partition walls (the percentage of the pore area or volume of the base material that is filled by catalytic material) is 10% or less, preferably less than 5%. The catalytic substance may comprise platinum and palladium in a ratio between 1:1 and 10:1. The filter may include an oxygen storage material, alkali metal or perovskite material. The catalytic substance may be included in a range between 10% and 50% of the total length of the partition walls in a lengthwise direction from the gas inflow-side end portion.
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