Why is plywood built up in layers?

Answer 1

Wood is made of fibres. These all run in the same direction. To a degree this is the materials weakness as in most cases wood breaks easier alone the fibre direction. By alternating the fibres in a differing direction (horizontal and vertically) this adds strength and prevents fibres easily breaking. In addition each layer has a powerful glue which binds the layers together

Answer 2

Plywood is probably the most popular and versatile man-made woodworking material available in home centers today. Plywood is a laminated product made up of numerous thin strips of wood laid in alternating directions and bonded with glue into strong, stable sheets. Because of this construction method, plywood is less susceptable to expansion and shrinkage.

By gluing numerous thin strips of wood in alternating directions layer by layer, plywood is much less likely to expand or shrink based on moisture in the environment, and the alternating construction creates a board that is much stronger in each direction than a similarly sized board cut from a single tree.

Most plywood is made from an odd number of layers, called plies (typically 3, 5 or 7), with an equal number of plies on each side of the center ply. In this manner, the surface plies are always parallel, and the grain of the surface plies usually follows the longest side of the sheet (although not always). The sheet is strongest parallel with (as opposed to against) the two surface plies.

Verifying site:

* http://woodworking.about.com/od/plywood/p/Plywood.htm

Answer 3

Plywood is layered in different directions to make the final plywood sheet stronger.