The lag time of a barrier film can be dramatically increased by the addition of scavengers which consume solute before it crosses the barrier. This increase in lag time theoretically depends on the location of the scavenger within the membrane. In this paper, we construct layered reactive barrier membranes to test this theory. The experiments show good agreement with the theory, which predicts that the lag time increase can be doubled over that of a homogenous reactive barrier membrane by confining the scavenger to the downstream interface. Computer modeling also supports this claim, but suggests that this increase may come at the expense of increased solute leakage prior to the lag time. Reasons for this leakage are discussed, with recommendations for balancing lag time and leakage increases. (c) 2005 Elsevier B.V. All rights reserved.