My supplier sent a bunch of samples of their label stock. The materials included various thicknesses of polyester, vinyl and other materials, as well as designation for color or b/w printing and adhesive permanence. All materials have photos of three year outdoor tests on their website. You can see the lower left polyester permanent adhesive thick material (rated to 304F), while not quite as white as the others, it matches the whiteness of the stock label letters well, and it clearly transmits the most light. Note the stock dash label on top of it and how we scaled the closely matched font type to also match the spacing properly for a totally stock look. Lighting provided by a flat EL Wire gizmo made for lighting up a bicycle. The good news is the nice thick stiff material transmits plenty of light and has a temp rating suitable for our application. The bad news is this material is $8.37 per sheet with a minimum purchase of 50 sheets. Yikes. They are sending me a sample sheet for free.