a lightweight board element includes a lightweight core , such as rigid plastic foam , and a covering layer such as glass fiber - reinforced resin . the upper and lower surfaces of the core are provided with a grid pattern made of up narrow grooves for improving stiffness and surface strength . the lower surface is provided with a further grid pattern of wider grooves which offer improved resistance to distortion . the cover layer is bonded to the core in a mold and the cover layer extends over the side edges of the core . the board uses relatively inexpensive materials and has excellent properties . the board element is particularly suited to the fabrication of a table tennis table in which case the grid pattern of narrow grooves in the upper core surface provides excellent ball bounce characteristics .