General purpose tubes are flexible tubes with an appearance similar to rubber hoses. They are mainly used for protecting wiring. Wiring is passed through the tube to protect them from abrasion and scrapes, while also insulating. The tubes come in colors such as clear, white, black, red, etc., that can be used for color coding by wire type. The materials used in the tubes include soft PVC, heat-resistant silicone, polyolefin resin, heat-resistant fluoropolymer, etc. Tubes that are made of flame-retardant polyolefin resin for use in harsh environments, tin-plated copper shield with 3 mm sleeve diameter that protects wire bundles from interference, as well as nickel-plated copper shield tubes are also available. Cable sleeving that fit tightly around the cable, such as heat shrink tubes and expandable tubes, are also available.