Plywood is a structural panel composed of multiple layers of thinner veneers of wood. It is used primarily as a load-bearing component of platform-frame–constructed buildings such as single-family and multi-family housing. It is used in wall sheathing, flooring and roofing applications. Particularly thick plywood with a special surface treatment is also used to line concrete forms in concrete-based construction.
In North America, softwood species are used to produce the veneer used in plywood. Thin veneers, typically 1/8- or 1/10-inch in thickness, are produced by a wide knife being advanced into a rotating log on a spindle. Layers of these veneers (usually an odd number) are glued together with the grain direction of adjacent layers perpendicular to each other. This arrangement of the veneers takes advantage of the natural directional strength properties of wood and produces a strong and stable panel with homogeneous properties throughout the panel.
Plywood is produced in varying thicknesses, depending on the thickness and number of veneers used; the most commonly used thickness is 1/2-inch. It is typically produced as 4x8-foot sheets. Plywood has good dimensional stability and may be sawn, nailed and glued like solid wood. Waterproof resins are used in manufacturing plywood, leading to a weather-resistant panel as long as the edges are not left exposed.