Moisture transport in fiber assembly is one of the critical factors affecting physiological comfort. It is useful to model bundle structure for understanding capillary flow in complex geometries representative of the void spaces formed between fibers. A new mathematical model MFB has been used to simulate alignment representative of void spaces formed between fibers in noncircular cross section fiber bundles. Fiber morphological character and their random packing pattern are emphasized to discuss the mechanism of capillary flow in fiber assembly in this work. Capillary equivalent radius distribution, flux of saturated fiber bundle, capillary generating ability, and wicking velocity are computed to predict which kind of shape is predominant for hydrophobic polyester fiber wicking. Vertical wicking model of polyester filaments bundle predicts that as the nonroundness of filaments increase, the maximum liquid height, flux of saturated bundle, and capillary forming ability will increase, while instantaneous wicking velocity increases not stably. Concave polygon shape of fiber bundle has much more small capillary tubes than convex shape of fiber bundle. (c) 2006 Wiley Periodicals, Inc.