Commercial Plywood is an engineered wood product made from three or more 'plies' or thin sheets of wood. These are glued together to form a thicker, flat sheet. The logs used to make plywood as a building material are prepared by steaming or dipping in hot water. They are then fed into a lathe machine, which peels the log into thin plies of wood. As each plywood sheet is usually between 1 and 4mm thick.