Plywood

Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that are glued together with adjacent layers, having both glued with each other at right angle. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboard (MDF), oriented strand board (OSB), and particle board (or chipboard).

All plywoods bind resin and wood fibre sheets (cellulose cells are long, strong and thin) to form a composite material. This alternation of the grain is called cross-graining and has several important benefits: it reduces the tendency of wood to split when nailed at the edges; it reduces thickness swelling and shrinkage, providing improved dimensional stability; and it makes the strength of the panel consistent across all directions. There is usually an odd number of plies, so that the sheet is balanced—this reduces warping. Because plywood is bonded with grains running against one another and with an odd number of composite parts, it has high stiffness perpendicular to the grain direction of the surface ply.

Smaller, thinner, and lower-quality plywoods may only have their plies (layers) arranged at right angles to each other. Some better-quality plywood products by design have five plies in steps of 45 degrees (0, 45, 90, 135, and 180 degrees), giving strength in multiple axes.

The word ply derives from the French verb plier,^[1] "to fold", from the Latin verb plico, from the ancient Greek verb πλέκω.^[2]

^ Collins Dictionary of the English Language, 2nd edition, London, 1986, p. 1181.
^ Cassell's Latin Dictionary, Marchant, J. R. V, & Charles, Joseph F. (eds.), Revised Edition, 1928, p. 421.

[1] Collins Dictionary of the English Language, 2nd edition, London, 1986, p. 1181.

[2] Cassell's Latin Dictionary, Marchant, J. R. V, & Charles, Joseph F. (eds.), Revised Edition, 1928, p. 421.

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