The structures of the cellulose nanofibers were characterized by TEM after negative staining by PTA. The samples obtained via different nanofibrillation methods and from various raw materials exhibit similar morphologies (Fig. 2). TEM images show the presence of very long nanofibers with varying degrees of entanglement. The widths of single nanofibers are mainly in the range of 2–5 nm (Fig. S1). In higher plants, the diameters of single elemental fibrils are reported to be ∼3 nm (Somerville et al., 2004).