Electrical tape, which comes in strips that are smooth on one side and sticky on the other, is used to insulate wires. Electricians always have electrical tape in their tool boxes.
While electrical tape comes in many colors, used to color-code different wires, the most common type is glossy black. It's thicker than masking tape and usually made of vinyl, with an adhesive surface that sticks to electrical wires and cords. Electrical tape safely insulates wiring, preventing electrical currents from passing to other wires, which can cause a fire.