The most commonly used form of twisted pair is unshielded twisted pair (UTP). It consists of color-coded copper wires, but does not include any foil or braiding as insulator to protect against interference. The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The following figure shows the different categories of UTP cables.