In reality, a CD is almost entirely made of polycarbonate plastic. A CD's surface is reflective because the disc is covered with a small coating of aluminum or, in some cases, gold. The gleaming metal coating reflects the laser needed to read or write data to the gadget. Without this metal coating, the laser would pass right through the plastic and out the other side. The aluminum used to coat the discs comes from aluminum cans. When burned, the plastic inside the can melts and flows together into a smooth layer on the outside. The aluminum stays solid, so it doesn't burn up when the disc is played back in the player. Although plastic has become the favorite material for compact discs, they used to be made of vinyl. Like a record, a vinyl disc has grooves that hold the music within its surface. The difference between the two materials is that records play one song after another, while CDs can store many songs on one disc. This means that you can take your collection with you wherever you go! Vinyl is a form of plastic. It is made by melting fat and wood pulp with sulfuric acid and sodium sulfite. As the mixture cools, it forms rods that are stretched and hardened into shape. These rods are cut into singles (the individual songs) or stacked together to make an album. The first CDs were actually audio tapes.