An article is provided that includes a core including a plurality of triangular core members. Two or more edges of each triangular core member are each attached to respective edges of other triangular core members in the plurality of triangular core members by respective hinges in a plurality of hinges. Each hinge in the plurality of hinges joins respective edges of a respective pair of substantially adjacent triangular core members in the plurality of triangular core members, is of a length to provide an offset between the pair of triangular core members, has a thickness less than thicknesses of the pair of triangular core members, and is integrally connected to the pair of triangular core members.