Synthetic fiber that are capable of spontaneously transporting water on their surface satisfy the equation wherein .theta..sub.a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment, if any, X is a shape factor of the fiber cross-section that satisfies the following equation ##EQU1## wherein P.sub.w is the wetted perimeter of the fiber and r is the radius of the circumscribed circle circumscribing the fiber cross-section and D is the minor axis dimension across the fiber cross-section, and wherein the uphill flux value of said fiber is from 2 to 60 cc/g/hr when measured from a reservoir of synthetic urine test fluid along a 20 cm long ramp to an absorbant on an attached platform at 10 cm height
