Young and colleagues proposed Youngs model of wetting that relates the contact angle of a water droplet on a flat surface to the surface energies of the water, the surface, and the surrounding air. This model is typically an oversimplification of a water droplet on an ideally flat surface. This model has been expanded upon to consider surface roughness as a factor in predicting water contact angle on a surface. Youngs model is described by the following equation:
 = Contact angle of water on the surface
= Surface energy of the surface-air interface
= Surface energy of surface-liquid interface
= Surface energy of liquid-air interface