Multilayer coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. Coextrusion avoids the costs and complexities of conventional multistep lamination and coating processes, where individual plies must be made separately, primed, coated, and laminated. Coextrusion readily allows manufacture of products with layers thinner than can be made and handled as an individual ply. Consequently, only the necessary thickness of a high-performance polymer is used tomeet a particular specification of the product. In fact, coextrusion has been used commercially to manufacture unique films consisting of hundreds of layers, with individual layer thicknesses less than 100 nm (1).