Similarly, wood supports respond significantly to changes in RH. Wood grains tend to swell perpendicular to the grain axis when they are exposed to moisture. As a wet ground layer is applied to the surface of a wood support, the wood in contact with the layer swells while the back of the panel remains unchanged. This can contribute to cupping, in which the panel of wood starts to bow transverse to the wood grain. The increased strains on the convex side of the cupped wood panel causes further fracture in the ground layer as it dries.