Moisture ingress into photovoltaic modules can be detrimental to the expected lifetime of the photovoltaic device. Hence, better understanding of this process and ways to predict the lifetime of a module are of high importance. Moisture ingress occurs through the polymeric materials used in a PV module, especially through the encapsulant which contacts all the sensitive parts in the module. In this work material parameters of polyvinyl butyral, an encapsulant mostly used for glass-glass modules, are presented and an examination of its lateral moisture transport and uptake behavior was undertaken to attain parameters for use in simulations. The uptake of moisture followed Fickian behavior. The absorption isotherm found was of Type III according to the classification by Brunauer, Emmett and Teller. (C) 2015 Elsevier B.V. All rights reserved.