Cordierite porous ceramics are attractive materials for diesel particulate traps, but are sensitive to the thermal shocks provoked by the ignition of accumulated soot. The present paper reports an investigation on a commercial porous cordierite to be used as a substrate for catalysts in exhaust pipes. Samples have been subjected to thermal shock tests to study the response of these ceramics to the repetitive thermal shock that occurs within automotive systems during the regeneration processes. In particular the effect of thermal treatment on microstructure and mechanical propel ties has been examined and explained.