conventional toughening agents are typically rubbery materials or small molecular weight molecules , which mostly sacrifice the intrinsic properties of a matrix such as modulus , strength , and thermal stability as side effects . on the other hand , high modulus inclusions tend to reinforce elastic modulus very efficiently , but not the strength very well . for example , mechanical reinforcement with inorganic inclusions often degrades the composite toughness , encountering a frequent catastrophic brittle failure triggered by minute chips and cracks . thus , toughening generally conflicts with mechanical reinforcement . carbon nanotubes have been used as efficient reinforcing agents in various applications due to their combination of extraordinary mechanical , electrical , and thermal properties . moreover , nanotubes can elongate more than 20 % without yielding or breaking , and absorb significant amounts of energy during deformation , which enables them to also be an efficient toughening agent , as well as excellent reinforcing inclusion . accordingly , an improved toughening method is provided by incorporating nanotubular inclusions into a host matrix , such as thermoset and thermoplastic polymers or ceramics without detrimental effects on the intrinsic physical properties of the matrix .