In foam cored sandwich composites, it is crucial to understand micromechanical characteristics of foam in relation with its properties to understand synergetic effects of adding nanomaterials such as CNTs. In this study, effects of CNT dispersion and distribution on cell morphology and foamability of rigid polyurethane (PU), which is directly related to microstructure and mechanical performance of overall structures were investigated. Raw and functional CNTs were added to rigid polyurethane foams up to 0.2 wt.% and their compressive strength is evaluated. The results showed that dispersion media such as PMDI with low viscosity revealed a better CNT dispersion and resulted with an enhancement of 13% in compressive strength compared to neat PU foams. This enhancement in foam core properties reflected in sandwich composites with an enhancement approximately 30% in both core shear and face ultimate strength. Hence, core shear found to be the common failure mechanism for all sandwich composites.