In CD-R, the organic dye sandwiched between the polycarbonate substrate and the metalized reflective layer of the media. CD-Recordable discs do not have any data on them until they are recorded. Instead the recording laser selectively melts "pits" into the dye layer -- but rather than burning holes in the dye, it simply melts it slightly, causing it to become non-translucent so the reading laser beam is refracted rather than reflected back to the reader's sensors. In pressed CDs, the data layer is part of the polycarbonate substrate, and is pressed into the top side of it by a "stamper" during the injection moulding process.