What are some products that require multi-layer coating?

What are some more products that require multi layer coating? An example would be X-ray film. Any thing that require multiple passes on a single layer coated? I know some products such as battery film, or protective covers for phone screens. What are some more of these products? Preferably technology that’s not being phased out... such as X-Ray film.


Cell Phones, TV's, Computers, display screens, solar cells...


X-ray film is being phased out due to digital radiography. Lenses are commonly multi-layer coated to improve transmission. Update: Depending on what you consider a coating... * printed circuit boards are often plated with gold. Nickle is plated on the copper, then gold over the nickle. This prevents intermetallics from forming between the gold & copper. Gold is a nasty substance with many bad properties for electronics. * Many coatings (anti-foulants used on ships, polyurethanes, ...) require a tie-coat (primer) between the base material and the actual coating. The tie-coat is formulated to have good adhesion to both materials. * House paints do better if a primer layer is used. * Automobiles often use a clear coat over the paint. Autos have a primer coat, paint coat, clear coat. * Optics will use multi-layer coatings to give desired characteristics (narrow band filters). * Camera filters are coated with nano-coatings to provide protection for the AR coatings and provide low surface energy so dust doesn't stick to the filter and finger prints are easy to wipe off (see B+W filters).