A compact disc is constructed of 5 separate layers…
1. First there is a thick, soft, clear plastic layer. This layer comprises the majority of the CD’s thickness and weight. It serves two purposes. First, it protects the data layer from damage on the play side and secondly it acts as a lens to focus the CD player’s laser onto the data layer so it can more easily read the data (much the way lenses in spectacles help eyes focus on the words on a page).
2. Next the data layer is where the music and any other information are stored. It’s the layer that the CD player “reads” in order to create the music, graphics, etc. The data layer is molded or pressed into the top of the clear plastic layer. The data in the data layer is arranged in tracks that spiral like the grooves on a vinyl record (except CDs are read from the “inside out”, the opposite of vinyl records).
3. Now a reflective, metallic layer is located on top of the data layer. It allows the disc to function like a mirror, reflecting the CD player’s laser back to the detector in the CD player after it reads the data layer It’s this layer that gives the CD’s play side a shiny appearance.
4. A thin, hard protective layer is an ultra-thin plastic coating that is added to provide some protection for the reflective and data layers, while also forming a surface upon which the label information can be printed.
5. Finally the label layer is printed on top of the protective layer. It contains the title, graphics, band and other information to identify the contents of the disc. (label side).