Different micromechanical models which account for the presence of dispersed and agglomerated nanofillers, specifically carbon nanotubes (CNTs) and cellulose nanowhiskers (CWs), in a polymeric matrix and consider the effect of a percolation threshold on the elastic modulus of the composite are derived and compared. We demonstrate that the critical filler volume fraction where a percolating network is forming marks a turning point in the reinforcement efficiency. The suitability of these models is verified by comparing simulated values with experimental data from literature. The results show that the models are able to predict mechanical properties over a wide range of testing conditions. POLYM. ENG. SCI., 2013. (c) Society of Plastics Engineers