This paper has demonstrated that interpenetrating composites could be designed to not only have an significantly enhanced
Young�s modulus, but also have a Poisson�s ratio at a desired value (e.g. positive, or negative, or zero). It is
found that when the effect of the Poisson�s ratio is absent, the Young�s modulus of interpenetrating composites is closer
to the Hashin and Shtrikman�s upper limit than to their lower limit, and much larger than the simulation and experimentally
measured results of the conventional isotropic particle or fibre composites. It is also illustrated that at the nanoscale,
the interphase can either strengthen or weaken the stiffness, and the elastic properties of interpenetrating composites are
size-dependent
