Plywood is made from thin sheets (veneers) of wood glued together, each with its grain in perpendicular directions in alternating layers to improve the strength and to minimize movement in the plane of the board. It's a widely used building material due to its many useful properties as well as its economic cost. High quality plywood sheets tends to be very strong and does not warp or crack under changes in atmospheric moisture, thus making it a reliable material for a wide variety of applications.