The invention relates to a honeycomb monolithic element for the filtration of particles, characterized in that the peripheral channels forming part of the outer wall of said element are configured to help in the formation of an outer wall whose inner face is substantially flat over the whole length of the element and in that said flat wall also has an increased thickness at the corners, so that, on a cross section, the ratio R of the thickness Ec of the wall, measured along the bisecting line of the angle at a corner of the element, over the minimal thickness Emin of said wall is greater than 1.5.