The quasi-static fracture toughness of nanocomposites is plotted as a function of CNT content in Fig. 8, clearly indicating positive effects of CNTs on fracture resistance of both composites with and without CNT alignment. For all CNT contents studied, the fracture toughness was consistently higher in the composites with alignment than those without. The largest improvement of about 51% compared to the neat epoxy was noted at 0.3 wt% CNT content, which also coincides with the highest efficiency in modulus improvement (Fig. 7). The corresponding improvement diminished at 0.5 wt% CNT content due to the reduced effectiveness of alignment at higher filler concentrations.