A ceramic honeycomb structure having reduced stress joints between its webs and skin is provided. The webs define a plurality of cells, and the skin surrounds the plurality of webs and has an inner wall that is connected to peripheral ends of the webs such that a plurality of angularly spaced wall joints are formed. Portions of the inner wall disposed between the angularly spaced wall joints include continuous arches. Each of the arches includes a curved central portion that terminates on either end on curved corner portions that are more sharply curved than the central portion. The arches eliminate sharp angles faces between the peripheral ends of the webs and the inner wall of the skin, thereby reducing stress concentrations in the interface between the webs and the skin. The arches also strengthen the skin, which allows it to be made thinner, thereby reducing thermally induced stresses in the joints between the webs and skin.