A mesoscopic computational model for polymer networks and composites is developed as a very coarse-grained representation of the network microstructure. Unlike more complex molecular dynamics simulations, the model network is static unless undergoing deformation. The elastic modulus, which depends only on the crosslink density and parameters in the bond potential, is consistent with rubber elasticity theory, and the network response satisfies the independent network hypothesis of Tobolsky. The model, when applied to a commercial filled silicone elastomer, quantitatively reproduces the experimental permanent set and stress-strain response due to changes in the crosslinked network from irradiation. (C) 2009 Elsevier Ltd. All rights reserved.