Warpage is a form of distortion that can occur in some materials, such as wood or plastic. This usually results from uneven stresses that can be internal or external to the material being warped. Common causes of warpage include uneven physical pressure or extreme temperature conditions placed on a given material. Sometimes, especially in woodworking practices, warpage specifically refers to a distortion from flatness; this is a problem when one needs a straight, flat board. In its most general sense, however, the term refers to any distortion from the intended shape and design of an object.
In man-made materials, warpage is often caused by residual stress in the composition of a material. Sometimes, flaws in production such as uneven cooling after manufacture or uneven distribution of molecules throughout a material cause internal stress that can lead to warpage or, in some extreme cases, cracking and further damage. Expansion and contraction of molecules occurs naturally with temperature change; problems with this occur when the expansions and contractions are not, for whatever reason, uniformly arranged throughout the material.
For many different manufacturing and shipping companies, it is very important to prevent warpage, as it can render products useless. As a very simple example, a warped board is often useless when a straight and flat board is needed; wood warping costs the logging industry millions in US dollars (USD) each year. Sometimes, warp on a product can even lead to eventual cracking and further damage to the material. Because of this, companies generally work to keep their products at relatively constant temperatures, as extremes of heat and cold can very easily cause an object to warp. They also make sure to keep products arranged in such a way that prevents excessive pressure from being placed on them.
A warpage can occur in many different ways and is described in terms of the way in which something warps. In a bow warp, for example, material becomes bent along the length of its face, giving it the curve of a bow. In a cup warp, the edges of the face of the material curve upward and are higher than the middle. A twist warp results in the two ends of the material being tilted at different angles to each other. A kink refers to a small area of warpage in which only a small part of the material is affected; this is often caused by a knot in a piece of wood or some similar imperfection.