 Cassie–Baxter state

A Cassie–Baxter state is a composite wetting state in which a drop contacts solid asperities over area fraction $f_s$ and trapped gas over the remainder. An ideal area-weighted contact-angle model gives the displayed apparent angle from the smooth-solid Young's equation angle ${\theta }_Y$. Reducing solid contact can strongly enhance apparent hydrophobicity. Such a state can be metastable and can collapse when liquid enters the texture; roughness alone does not guarantee it.