The WRV (water retain value: g H2O retained by whizzed (3000 g, 15 min) fibers per g abs. dry fiber) indices, viz., initial WRVo (e.g., 90-120%, volume of capillary system, i.e., compactness of unbeaten fiber structure), limiting WRVgr (level-off value for beaten fibers), and WRVn (internal fiber fibrillation in nth beating cycle), were used to follow fiber fibrillation in terms of the equation WRVn = WRVgr - (WRVgr - WRVo)beta(n), where beta is a coefficient characteristic of the beater used, adjusted by successive approximations. The equation developed requires industrial verification. It enables the beating process to be objectively optimized.