A cable is one or more wires or optical fibers bound together, typically in a common protective jacket or sheath. The individual wires or fibers inside the jacket may be covered or insulated. Combination cables may contain both electrical wires and optical fibers. Electrical wire is usually copper because of its excellent conductivity, but aluminium is sometimes used because it is lighter or costs less.
Electrical cables may be made flexible by stranding the wires. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility. A thin coat of a specific material (usually tin-which improved striping of rubber, or for low friction of moving conductors, but it could be silver, gold and another materials and of course the wire can be bare - with no coating material) on the individual wires. Tight lays during stranding makes the cable extensible (CBA - as in telephone handset cords).