The cylindrical filter element consists of many square parallel channels running in the axial direction, separated by thin porous walls. The channels are open at one end, but plugged at the other. This way the particle laden exhaust gases are forced to flow through the walls.
Gas is able to escape through the pores in the wall material.
Particulates, however, are too large to escape and are trapped in the filter walls. A proprietary catalyst is coated onto the inside surface of the filter monolith. The catalyst lowers the soot combustion temperature allowing the filter to regenerate. The accumulated soot is oxidized in the filter during regular operation of the engine. The catalyzed filter monolith is wrapped in a fiber mat and packaged into a stainless steel housing, which is installed in the vehicle's exhaust system.