text: A way to experimentally determine wetting is to look at the contact angle (), which is the angle connecting the solid–liquid interface and the liquid–gas interface (as in the figure).
  : If , the liquid completely wets the substrate.
  : If , high wetting occurs.
  : If , low wetting occurs.
  : If , the liquid does not wet the substrate at all.
  The Young equation relates the contact angle to interfacial energy:
  where  is the interfacial energy between the solid and gas phases,  the interfacial energy between the substrate and the liquid,  is the interfacial energy between the liquid and gas phases, and  is the contact angle between the solid–liquid and the liquid–gas interface.