Superhydrophobic Finish Contact Angle & Roll-off Predictor

The Cassie state is metastable, and that is the practical problem with superhydrophobic textiles rather than a footnote to it. Pressure, impact, condensation within the texture or a surfactant in the water can all collapse the drop into the Wenzel state, at which point the same surface becomes more wettable than a smooth one would have been — which is why the Wenzel angle is shown alongside. A Wenzel result of 180 degrees means the roughness term is out of range and that state is simply not defined for this combination. Roll-off assumes a drop large enough for gravity to matter and a uniform texture; small drops pin regardless of angle. Durability is the other omission — texture that survives a laboratory drop rarely survives abrasion and laundering.