What is "Warping"?

• There are several forms of warp, including bow, cup, twist, crook, oval and diamond warps; however, essentially, all warp is broadly defined as any deviation from flatness in a plywood board. The opposing forces of shrinking and swelling must balance one another out in order for plywood panels to remain flat. Ideally, for best use, all surface points lie on one plane. Warp-prone plywood is less effective in all applications and its presence often leads consumers to seek alternative species or products.
  
  

Contributing Factors

• Moisture content and distribution varies from glue set and throughout the life of the plywood, which stresses the board. The more extreme the moisture difference, the more likely the plywood is to warp. Often, wood fibers within the plywood cannot keep pace with the internal moisture content release rate of the sapwood, resulting in dimensional instability, warping, cracking and twisting. Relative differences in shrinkage rates as pieces dry will also encourage warp, as will the presence of young or irregular grained wood.
  
  

Minimizing Warp

• While most of the issues associated with warp are due to problems in the plywood construction or intrinsic to the sap wood lumber itself, consumers can play a role in minimizing warp. Keep yellow pine plywood out of rain and direct sunlight prior to use. Plywood sheets expand when wet and shrink when dry. Over time, repeated expansion and contraction can lead to warping or cracking in the wood. Overall, properly stored plywood is less likely to warp.
  
  

Alternatives

• Wood warp is one of the most significant challenges facing the timber industry. While yellow pine plywood still makes up approximately 60 percent of the total domestic plywood market, the use of oriented strand boards is steadily growing in acceptance. OSB is an engineered wood panel that is composed of waterproof, cured wood. It is arranged in cross-oriented layers, similar to traditional plywood. The production of OSB is highly automated and produces very high yields using a wide range of small, fast-growing trees. It may incorporate desirable features, such as slip-resistant texture, but it is less impact-resistant than yellow pine plywood.