Abstract: A process modifies the surface diffusion and wetting characteristics of a microporous material such as active carbon or silica, by applying a plasma of polymer precursor monomers to an external surface of the material to modify its adsorption properties, the microporous material obtainable thereby being modified by presence of a nanolayer of polymeric material extending over said external surface around the pores to partially occlude pore openings to a predetermined extent, but the nanolayer does not substantially infiltrate the pores of the microporous material.