Vinyl, a type of plastic, breaks down and dries out over time when exposed to ultraviolet light and weather. This is a natural process of deterioration as chemical bonds in dyes break down and oils used to make vinyl volatilize, or pass out of, the plastic as a vapor. Dyes also break down at different rates, depending on color. Often the chemical breakdown — or oxidation — of plastic leaves behind a chalk-like residue that lends a whitish appearance to the color, making it look bleached. One solution for dry, faded plastic is to use a vinyl restorative product on it.
Clean off any superficial dirt from the vinyl decals with a soft cloth and a solution of detergent and water. Substitute a sodium percarbonate cleaner such as OxiClean for the detergent if decals have mildew or mold on them. Do not rub hard or use a scrubbing pad, or you may damage the decals.
Rinse the decals with clear water and allow them to air dry completely.
Wipe with rubbing alcohol dabbed on a soft cloth to ensure an absolutely clean surface.
Apply a vinyl restoring product such as ArmorAll Original Protectant, Vivilon Envirolon, Vinyl ReNu or similar product with a cloth, brush or spray apparatus — in accordance with the manufacturer's directions for application.