The lifetime of organic solar cells is a critical point limiting their marketability. To extend this lifetime, these devices rely on ultra-barrier materials to prevent their oxidation by oxygen and moisture. Production costs of this barrier material should nevertheless remain in accordance with the low price of the devices. The aim of this work is the development of a multilayer gas barrier material adapted to the device requirements, relying on low cost wet processes. Oxygen and water vapor permeability of organic/inorganic multilayer materials obtained on polymer substrates has been studied. In this paper we also demonstrate that fast helium permeability measurements may be used to screen water barrier performances of thin inorganic layers on polymers in a short time span. Different multilayer composite structures were tested. The potential of such materials as encapsulation material for organic solar cells has been investigated. We demonstrate in this paper that a few layers with a minimum of process steps are sufficient to enhance the stability of P3HT:PCBM organic solar cells under illumination, limiting the efficiency loss to about 10% over 450 h. (C) 2013 Elsevier B.V. All rights reserved.