This specification covers honeycomb core made of polymide paper sheets in a non-hexagonal, flexible cell configuration and supplied in the form of blocks, slices, and ordered shapes. This honeycomb core has been used tyipcally in sandwich structures in single or compound curvature parts requiring high strength and corrosion resistance in the temperature range -55 to +82 degrees C (-67 to +180 degrees F) but usage is not limited to such applications.