The control of the wettability by nanoparticles (NPs) was studied by treating lignin model surfaces with silica NPs at various NP concentrations The experimental contact angles (CAs) were compared to a modified Wenzel equation, which takes into account the changes in the effective sui face area and the surface roughness The conclusion was drawn that the change of effective roughness is not visible, which implies that the NP-induced geometric heterogeneity is irrelevant for the CA change This is attributed to dynamics of contact line in the weak pinning regime