The shapes of stress–strain curves for three phase composites were almost linear. Table 13.1 shows the averaged test results of modulus for all types of CNF/CF/epoxy composites. It was found that the longitudinal modulus is not seriously affected by the CNF dispersion. On the contrary, transverse modulus is more affected by CNF dispersion. Three-phase composites with 0.5 and 1 wt% of CNF showed increases in transverse modulus of about 10.8 and 14.9%, respectively.