The ability to produce polymer nanocomposites, which comprise a percolating, three-dimensional network of well-individualized nanofibers, is important to maximize the reinforcing effect of the nanofibers. While microcrystalline cellulose (MCC) has been previously shown to improve the mechanical properties of polymer composites, the formation of fibrous percolating networks within the nanocomposites has been stifled. Through the utilization of a template approach, nanocomposites based on an ethylene oxide/epichlorohydrin copolymer and nanowhiskers isolated from MCC were produced that display the maximum mechanical reinforcement predicted by the percolation model.