A wettability study was performed on samples of alfa fibers with the Wilhelmy plate technique. The set of test liquids employed in the measurement of the contact angles was composed of water, heptane, diiodomethane, alpha-bromonaphthalene, and formamide. During their first immersion in high-surface-energy test liquids, the alfa fibers showed anisotropic behavior: they had an advancing contact angle of 67 +/- 6 degrees in one orientation of immersion and an angle of 112 +/-9.5 degrees in the opposite one. Optical microscopy revealed the existence of fibrils on the alfa-fiber surface. They kept almost the same orientation and were responsible for the interesting hydrophobic/hydrophilic behavior of the fibers. Contact an-le measurement and investigations of the hysteresis were also performed. The various results were examined according to the heterogeneities of the fibers. The Surface energy of the alfa fibers was determined with three theoretical models: the geometric model, the Good-Van Oss-Chaudhury model, and the Chang model. A comparative study of these models was undertaken. The study of the wetting properties of alfa fibers will provide essential information for optimized composites and so will help us in choosing the right chemical treatment necessary to enhance adhesion in alfa-fiberbased composites. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3322-3327, 2008