The process of creating plywood is complex and can vary widely depending on the product. In some products, plywood is produced with a lumber core, but all-veneer plywood is much more common. In either case, the thickness and grain orientation of each veneer is matched with a veneer on the other side of the central piece, resulting in an odd number of layers. Occasionally, the central layer may consist of two veneers glued together with parallel grain directions, resulting in an even number of layers. Its resistance to warping and splintering and its uniformity of strength is increased by varying the orientation of the grain.
The panels are spread with glue and assembled such that the direction of the grain varies between layers. The outer layers are called the face and the back, the inner layer is called the core, and the layers between are called crossbands. In standard construction, the crossbands run perpendicular to the face, back, and core, allowing for maximum strength and stability. In some cases, alternating plies may be placed at 45-degree angles. The stacked plies are then loaded into presses.
