The oxygen barrier behavior of polymer films can be significantly improved by incorporating particles of an oxygen-scavenging polymer, e.g., those based on butadiene containing an appropriate catalyst, in a matrix of a barrier polymer like poly(ethylene terephthalate) or polystyrene. This paper develops a mathematical model for predicting the transient barrier properties of such blend films. The analysis uses a "shrinking core" model for oxygen consumption by the particles and treats oxygen diffusion in the matrix polymer by a one-dimensional approximation. Scavenging can extend the time lag for the transient permeation by factors of thousands. A key point of the analysis is the calculation of the flux of oxygen exiting the downstream surface of the film for times of the order of the time lag and less using realistic geometrical and physical parameters. (c) 2008 Elsevier B.V. All rights reserved.