Abstract: When conventional honeycomb structures are formed into cylinders, the inner wall made up of the inner edges of the individual honeycombs is circumferentially compressed and the outer wall made up of the outer edges of the honeycombs is circumferentially stretched. As a result, the height of the inner wall increases and the height of the outer wall decreases resulting in a bowing in of the central portion of the cylinder so that the cylinder assumes an hourglass shape. This bowing in can be avoided by corrugating the original ribbon core material in the manufacture of the honeycomb in such a manner that one longitudinal edge of the corrugated ribbon follows a wave form of an amplitude greater than the wave form defining the opposite longitudinal edge.