Abstract: Disclosed is a core for use in a core-board, which consists of an embossed sheet of a light weight material comprising a central surface extending in a plane and a plurality of embossments called top and bottom cells, that are identical in shape and project from the central surface on both sides thereof. Each of the top and bottom cells is integral to the central surface and of pyramidal shape. Each of them also has an open base of regular hexagonal shape extending in the plane of this central surface and a top flat surface of regular hexagonal shape and of a smaller surface area than the base. These top and bottom cells are regularly distributed onto the central surface in such a manner that each top cell is not adjacent to another top cell but extends edge to edge to three spaced apart bottom cells, and each bottom cell is not adjacent to another bottom cell, but extends edge to edge to three spaced apart top cells.