The effect of residual lignin and heteropolysaccharides in CNF and nanopapers was studied by Ferrer et al. [239].For this study, CNF were produced from both bleached and unbleached, oxygen-delignified birch fibers as starting materials. Interestingly nanopapers produced with CNF from unbleached fibers presented higher densities when compared to nanopapers produced from bleached pulps. It was due to the higher fibrillation degree achieved in unbleached fibers, thanks to a higher content of hemicelluloses.Moreover, stress at break and energy absorption was higher in the nanopapers made from unbleachedfibers CNF.