All wood based panels which are dry to the touch will shrink and swell as atmospheric conditions around them change. The amount of change is dependent on how high or low the humidity and temperature are, relative to typical conditions, and how long the adverse conditions last.   The dynamic nature of the system will cause moisture gradients within panels and these can lead to internal stresses caused by differential swelling or shrinking. This can result in delamination and splitting, most often seen in veneer based products like plywood. It can also cause warping if one side has swollen or shrunk more than the other.   Warping is a general term used to describe any movement that causes a panel to lose its shape. Cupping is generally associated with flooring where the edges are raised above the middle of the panel and crowning is the opposite of this. Twisting describes the warping in the plane of a panel such that at least one corner is higher than the others. Bowing is curvature of the face. Crook or spring is a curvature of the panel edge. This last type is rare in wood based panels and where it does occur is often associated with inaccurate machining rather than moisture-induced distortion.   Warping, and in particular bowing, can also occur if the panel is not symmetrical through its thickness. For example particleboard that has been sanded more on one face than the other or OSB where the top surface layer is thicker than the bottom.   The amount of differential shrinkage or swelling required to cause warping can be very small. Take for example a flooring product that is 100mm wide and 1.4m long with a 10mm bow in the middle. The difference in length between the bottom and upper face can be estimated via simple trigonometry (see diagram). The sum of the two hypotenuses will provide a rough estimate of the swelling required in the top face to cause 10mm of bow. In this case, the two hypotenuses add up to 1400.143 when rounded to three decimal points. This tells us that if the surface length swells by only 0.01% more than the bottom, we can expect a bow of 10mm.   Admittedly, this method underestimates the differential swelling required, but not by much.   This simple calculation also illustrates why it is important to have expansion gaps around the edges of floating floors.