This specification covers honeycomb core made of polymide paper sheets and supplied in the form of blocks, slices, and ordered shapes, the cells of the core being in an overexpanded, rectangular configuration. This honeycomb core has been used typically for bonded sandwich structures requiring high strength and corrosion resistance in the temperature range -67 to +180 degrees C (-55 to +82 degrees F), for use in single curvature parts, but usage is not limited to such applications.