A composition includes 50 to 95 weight percent of a thermoplastic polyurethane, and 5 to 50 weight percent of a particulate engineering plastic. The slot identification strategy is comprised of three components: functional group naming; functional group numbering; and functional group colour coding. The substrate is then moved through the hot gas stream at a velocity selected to sufficiently heat the surface of the substrate to a high temperature at which doping and diffusion processes can be done in an efficient manner, while a thermal gradient is preserved throughout the thickness of the substrate.