 A hydrophobic surface (one that has an original contact angle greater than 90°) becomes more hydrophobic when microstructured – its new contact angle becomes greater than the original.However, a hydrophilic surface (one that has an original contact angle less than 90°) becomes more hydrophilic when microstructured – its new contact angle becomes less than the original.Cassie and Baxter found that if the liquid is suspended on the tops of microstructures, "θ" will change to "θ"CB*

where φ is the area fraction of the solid that touches the liquid.