Such a universal, accessible, and versatile structural material plywood is. It is made by adhering an odd number of thin sheets (or “plies”) of soft- or hardwood together so that the grains of adjacent layers are arranged at right angles. This construction technique makes the material strong, and the plywood becomes stronger the more veneers are used. Plywood is graded for exterior or interior use depending upon the water resistance of the glue used to stick the plies together, and, depending on the finish of the exterior layer and the strength of the internal ones, uses for plywood vary from basic construction (sub-floors, millwork and roofs) to more refined purposes (furniture, wall panels and floors).
The smoothness of the surface and the number of defects in it give it its “grade.” Some types have beautiful graining on the exterior veneer, and — if thin enough — can be formed into curved shapes. Available at lumberyards and home centers, plywood is a commonly used material because it resists shrinking and cracking, while being lightweight and rigid. A wide variety of plywoods are made with the following variations: strength, thickness, species of plies, type of glue (interior, exterior, marine), and exterior ply finish quality.