Plywood is a type of engineered wood made from thin sheets of wood , called plies
or veneers. The layers are glued together, each with its grain at right angles to
adjacent layers for greater strength. There are usually an odd number of plies,
as the symmetry makes the board less prone to warping , and the grain on the outside
surfaces runs in the same direction. The plies are bonded under heat and pressure
with strong adhesives, usually phenol formaldehyde resin, making plywood a type
of composite material. Plywood is sometimes called the original engineered wood.
A common reason for using plywood instead of plain wood is its resistance to cracking,
shrinkage, twisting/warping, and its general high degree of strength. It has replaced
many dimensional lumbers on construction applications for these reasons.