A model is developed and solved analytically and numerically to describe the barrier properties of multilayer films with alternating reactive and inert layers. Incorporation of reactive scavenging sites in packaging materials can significantly improve their barrier properties. Due to mechanical and optical requirements, barrier films typically consist of polymer blends or multilayer films of the scavenging material and an inert supporting polymer. Because composite reactive barriers are expected to operate for months or years, purely experimental characterization is not practical and models are needed to optimize the configurations and to confidently extrapolate experimental data. The model for multilayer films is solved numerically over a wide parameter space, varying physical properties and layer configuration to determine the flux and time lag. Asymptotic analysis of the model is used to develop analytical predictions for transport behavior at early and long times. The performance of multilayer composites is compared to polymer blends and discussion of the most suitable configuration for different scenarios is presented. (c) 2012 Elsevier B.V. All rights reserved.