A low temperature (300 degrees C) CVI technique was employed to modify commercial sol-gel silica membranes, in order to repair defects often formed in their top sol-gel layer. Membranes were characterized before and after modification in terms of permeance and permselectivity with the use of He and N-2. The permselectivity of the sol-gel silica membranes varied between 3.2 and 52, while after the CVI treatment the permselectivity increased to 68-308. Moreover, a simple model was developed in order to estimate the defect concentration in silica membranes and assess their influence in the membranes performance. (C) 2009 Elsevier B.V. All rights reserved.