Flexible PVC/silica composite membranes having a porous structure have been produced using plastisol-plastigel technology. Equilibrium and rate studies related to water vapor adsorption on membranes have been studied using a Cahn 2000, gravimetric adsorption system. For the solubility and diffusivity of water vapor in membranes 4.23-7.74 cm(3)/(cm(3) cmHg) and 2.0-3.5 x 10(-13) m(2)/s values have been determined respectively. The measured permeability of water vapor through membranes 1.6-7.3 x 10(-6) ((cm(2)/s)/(cm(2) cmHg))cm, were much higher than predicted permeabilities 0.85-2.73 x 10(-8) ((cm(2)/s)/(cm(2) cmHg))cm. from solubility diffusion data, indicated the membranes had a porous structure. The membranes are suggested as a leather substitute since the permeability through membranes is comparable to that of leather and is at least 100 times higher than that of plasticized PVC film obtained by conventional processing techniques.