Honeycomb segment and honeycomb structure

A honeycomb structure unitarily formed and comprising porous partition walls separating and forming a plurality of cells functioning as fluid passages and having a structure where first cells each having an open end portion on one side and a plugged end portion on the other side and second cells each having a plugged end portion on the one side and an open end portion on the other side are alternately disposed so that the fluid flowing from the end portion on the one side where the first cells are open may pass through the partition walls and flow out into the second cells as a permeated fluid, and the permeated fluid can flow out from the end face on the other side where the second cells are open;

• wherein the first cell has a larger cross-sectional area than the second cell in a cross section cut along a plane perpendicular to the longitudinal direction,
• the first cells and the second cells are alternately disposed in a first direction and a second direction perpendicular to the first direction in a cross section cut along a plane perpendicular to a longitudinal direction of the cells, and
• an opening percentage of the first cells increases continuously or in stages from the first cell in a central portion in the cross section cut along the plane perpendicular to the longitudinal direction of the cells toward the first cells in a peripheral portion excluding incomplete cells in an outermost periphery in the cross section.