Similar to Casimir force, nanofibers have a potential that attracts water molecules, while the porosity of the nanofiber mat produces a repelling force. Wetting property of a nanofiber mat is a result of combination of the forces and gravity. A new concept, the geometric potential or the boundary-induced force, is introduced to elucidate the basic property of wetting. Various nanofiber mats with different fiber morphologies are fabricated by the bubble electrospinning. The paper concludes that superhydrophobic properties of nanofiber mat depends upon mainly fiber morphology and porous structure of the mat, hydrophilic properties of ZnO nanorods will not affect the water contact angle much.