A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data.

Most of a CD is composed of a plastic called polycarbonate. The bottom layer is a polycarbonate layer where data is encoded by using tiny bumps on the surface. Above this layer is a reflective layer typically made of aluminum (gold is also used, although quite rarely).

According to How Stuff Works, a CD is imprinted with pits and bumps which form a track that spirals out from the center of the CD to its edge. The pits and bumps that make up the spiral track are approximately 0.5 microns wide. Each track is separated by 1.6 microns (millionths of a meter) of space.