To reduce flow restriction of the wall flow type diesel particulate filters, the pore size distribution of DPF material was improved. Large pore material is preferred to reduce the flow restriction of the DPF. However pore diameter should be controlled within a certain limit to maintain high trapping efficiency against diesel particulates. In order to solve these conflicting matters, the mean pore diameter was enlarged from 13μm of the current material to 20 μm or more, while maintaining the cumulative volume of pores above 100μm within 8% of the total pore volume. The safe limit against thermal shock failure of the improved DPF material having 9″D x 12″/, 12.5/ volume was also determined using diesel burner regeneration system.