In order to determine the role of reinforcement-matrix interfaces in the infiltration of water molecules within a composite material, we introduced a very thin layer that was highly diffusive and trapping between reinforcements and matrix. A finite element discretization of such an extremely thin surface layer poses numerical difficulties. To resolve this problem, we sought to substitute this interfacial surface, whose thickness is very low, with a thicknessless interface which has equivalent diffusion behaviour. Using asymptotic development techniques, we also established a minimum interface limit which is asymptotically equivalent to the problem of moisture transmission through a very thin highly diffusive and trapping layer. Using the method of homogenization environments periodicals and model Langmuir, we determined hygroscopic behaviour equivalent to the syntactic foams while taking account of interface law proposed. Determination of the diffusion coefficients and trapping is then compared with the experimental results. (C) Koninklijke Brill NV, Leiden, 2010