In recent paper authors proposed “void dispersion method” to control more widely thermal expansion coefficients (CTEs) of composites materials. This method introduces microvoids in the matrix of composites and utilizes an interaction effect between the reinforcement and the microvoids which yields reduction of themal expansion coefficients. However the introduction of microvoids gives rise to various drawbacks, such as weakening interfaces and becoming sensitive to humidity in the air. Thus in this paper, effect of humidity in the air on porous composites has been examined. A skeletonized 3D composites were used as a typical porous composite. It was shown that the introduction of voids in the matrix leaded to wider specific surface and resulted in higher diffusion of water in the matrix. Main phenomena manifesting the water absorption effect were shown to be higher CTE in low temperature region and low glass transition temperature. As a measure to prevent the water absorption, galss coating on the surface of the porous composite was finally examined and it is shown to be effective under the low humidity environment.
