in order to inexpensive construction materials effectively utilizing timber resources and realizing any desired properties by using so - called low - quality materials including slim timbers , old timbers , wood cuttings produced by lumbering , bamboo , and so forth , wood , bamboo and other wooden source materials are split into fragments along their fibers by water vapor explosion , and such explosive - split fragments are shaped and hardened by adding an adhesive , mortar or expandable resin into a new wooden material such as multi - layered board , cement board or foamed resin board of explosive - split fragments . the explosive - split fragments are also usable in various fields other than fabrication of the new material .