While CD-ROM is one of the most durable data storage devices ever invented, they are not indestructible. To understand what can affect the quality and lifetime of a CD-ROM disc, we first need to look at how they are put together. All CDs are made up of several layers, as shown in this CD-ROM construction diagram. The thickest layer, sometimes called the substrate, is molded from polycarbonate plastic. (Yes, this is the same plastic used for bulletproof windows, although much thinner.)

The top of this substrate is where the pits are actually molded into. However, if drawn to scale, the pits would hardly be discernible because although the substrate is 1.2mm thick, the pits are only about 1/1000 that deep! On top of the pit surface, a thin layer of metal is deposited. This is what gives the disc its shiny look. This metal is most often aluminum, but some manufacturers use alloys to make the discs look golden, or even use actual gold. This layer is also very thin, but must be thick enough to reflect most of the laser light back to the drive so the discs can be read reliably. On top of the metal, a sealcoat layer is added to protect the metal from damage such as scratches and corrosion from the outside air. The disc label is then silk screened directly on top of the protective coat, completing the process.

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