Plywood is a sheet material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. Plywood bind resin and wood fibre sheets (cellulose cells are long, strong and thin) to form a composite material. The alternation of the grain is called cross-graining which has several important benefits:

  • Reduces the tendency of the wood to split when nailed at the edges;
  • Reduces expansion and shrinkage, providing improved dimensional stability; and it makes the strength of the panel consistent across all directions.
  • reduces warping. Because plywood is bonded with grains running against one another and with an odd number of composite parts, it is very hard to bend it perpendicular to the grain direction of the surface ply.