In part III of this series of articles, we present the analysis of transient permeation through two-layer reactive-passive (RP) film designs, the analysis extension to multilayer structures, and optimized design solutions for multilayer barriers incorporating immobile noncatalytic oxygen scavenger within one of the layers. The reduction of oxygen ingress into a package within a certain timeframe depends on two factors: extension of the scavenger exhaustion time and reduction of the transient transmission rate through the film during that time. The optimal design for the scavenger exhaustion time involves exposure of the reactive layer to the package contents and its protection from high levels of environmental oxygen by the best possible passive barrier layer. The film barrier properties can be further optimized by the selection of the matrix material to place the scavenger in. Reducing the initial transmission rate requires the placement of the scavenger within a layer with the lowest diffusivity of the matrix polymer. When one chooses between two layers with different material transport properties in which to put the scavenger, the optimal solution for the ingress depends on the desired time to provide an improved barrier. The lifetime of the scavenger in the RP film is shortened for design 1, when the diffusivity of the reactive layer is smaller than that of the passive layer, compared to RP design 2, with the layer matrix sequence reversed, but the transient transmission rate is greatly reduced on average for the former. If the desired time to provide a barrier does not exceed the scavenger exhaustion time for RP design 1, the lowest diffusivity material should be used as a matrix for the innermost layer loaded with the scavenger. Otherwise, the highest possible passive barrier should be placed into the film external layer to minimize the total ingress during longer times. (c) 2006 Wiley Periodicals, Inc.