* Polycarbonate substrate - the data layer consists of indentations (bits) in the substrate, made by a laser beam which melts the substrate
* Aluminium (or gold on some very early CDs) reflective layer which reflects the light from the laser (the aluminium layer is protected from oxidation and scratching by the polycarbonate layer)
* Lacquer layer - a protective coating to protect the data layer from dust and scratching