Patent ID: 7857885

Claim:
A filter comprising: a honeycomb structural body having a plurality of through holes extending parallel with one another in a length direction of the honeycomb structural body, the honeycomb structural body having a wall portion interposed between the through holes; and a sealing material layer formed on a circumference of the honeycomb structural body, wherein said plurality of through holes includes a plurality of large-capacity through holes and a plurality of small-capacity through holes, said large-capacity through holes and said small-capacity through holes being substantially same in numbers, said large-capacity through holes are sealed at one end of said honeycomb structural body, said small-capacity through holes are sealed at the other end of said honeycomb structural body, said large-capacity through holes and said small-capacity through holes have a ratio of partition wall length, α, and an aperture ratio, β, and said α and said β satisfy 0<α≦1.5, 2≦β≦2.75, and β≧(20/9)α 2 +1.