Low-energy surfaces primarily interact with liquids through dispersive (van der Waals) forces. William Zisman produced several key findings:
Zisman observed that cos θ increases linearly as the surface tension (γ) of the liquid decreased. Thus, he was able to establish a linear function between cos θ and the surface tension (γ) for various organic liquids.
A surface is more wettable when γ and θ is low. Zisman termed the intercept of these lines when cos θ = 1 as the critical surface tension (γ) of that surface. This critical surface tension is an important parameter because it is a characteristic of only the solid.
Knowing the critical surface tension of a solid, it is possible to predict the wettability of the surface. 
The wettability of a surface is determined by the outermost chemical groups of the solid.
Differences in wettability between surfaces that are similar in structure are due to differences in the packing of the atoms. For instance, if a surface has branched chains, it will have poorer packing than a surface with straight chains. 
Lower critical surface tension means a less wettable material surface.