Wetting tension is another way of describing the wettability of a solid surface. It is used as an alternative to surface energy. Unlike surface energy, wetting tension is exact and there are no assumptions or approximations. Wetting tension is, by definition,
liquid surface tension X cosine of contact angle
Since the value of the contact angle will range from +1, at zero degrees contact angle, to -1, at 180 degrees contact angle, the wetting tension will vary from the IFT of the liquid to -IFT of the test liquid. Now at this point you may ask: what good is that since the number depends on the test liquid? The answer is twofold:
wetting tension is often used in biological or medical studies where the liquids are aqueous anyway
wetting tension is linear in the cosine of the contact angle and this more accurately expresses the relative effects of variations in contact angle.
Additionally, wetting tension accurately conveys the force balance that exists between the cohesion of the liquid to itself and the adhesion of the liquid to the solid in the contact angle.
Finally, within the FTA software, if you wish to plot the cosine of the contact angle, set the IFT of the test liquid to 1.0 and plot wetting tension.