When a water droplet is on a surface that is not flat and the surface topographical features lead to a surface area that is larger than that of a perfectly flat version of the same surface, the Wenzel model is a more accurate predictor of the wettability of this surface. Wenzel's model is described by the following equation:
 = Contact angle of water predicted by Wenzel's model
 = Ratio of surface area of rough surface to the surface area of a flat projection of the same surface