A new in situ infusion method was used to incorporate small amounts (similar to 1 wt %) of metal and metal oxide particles into a polymer matrix. Nanosized particles were observed by both transmission electron microscopy and atomic force microscopy. Oxygen (O-2) and carbon dioxide (CO2) transport properties of the infused materials were investigated using a dynamic diffusion approach in which both testing and purge gases can be controlled. It was discovered that trace amounts (similar to 2%) of hydrogen (H-2) in the purge gas were sufficient to considerably reduce the O-2 flux of FEP films infused with palladium (Pd) nanoparticles, up to a 200-fold decrease. In contrast, H-2 essentially had no effect on the transport of CO2. The generality of the remark-able reduction in oxygen flux was also demonstrated with films of PP, LLDPE, PET, and nylon 6,6 infused with Pd nanoparticles. This oxygen-scavenging effect became more pronounced at lower oxygen concentrations. The catalytic role of I'd in the reaction of O-2 and H-2 and the enormous surface area provided by the dispersed nanoparticles were responsible for this highly efficient oxygen-scavenging effect. (C) 2004 Wiley Periodicals, Inc.