Geosynthetic clay liners have a tremendous record as hydraulic barriers in engineered lining and capping systems. Still, they are not well understood by the larger geotechnical design community. They require knowledge not only of geosynthetics but of sodium bentonite types, behavior, and suitability in certain applications. Dr. Craig Benson, Professor Emeritus at the University of Wisconsin – Madison, is one of the most versed researchers in the world on GCLs and bentonite-polymer composites. These composite materials are changing the way we view GCLs and how they can be used beneficially and most effectively in aggressive environments requiring barrier support.