In this study we experimentally determined the length distributions of the fiber bundles after each drawing. The detailed analysis of bundles lengths distributions before and after each drawing made it possible to understand the modes of rupture and to determine their kinetics of shortening and refining. Interestingly, the refining of the rovings is accompanied by a decrease in the rate of bark (set of very hydrophilic compounds), which will promote the wetting of the fibers by the polymer during the implementation of the composite and thus will improve significantly the hydric behavior of the material.