Heat shrinkable tube is a shrinkable plastic tube used to insulate wires, providing abrasion resistance and environmental protection for stranded and solid wire conductors, connections, joints and terminals in electrical work. It can also be used to repair the insulation on wires or to bundle them together, to protect wires or small parts from minor abrasion, and to create cable entry seals, offering environmental sealing protection. Heat shrink tubing is ordinarily made of nylon or polyolefin, which shrinks radially (but not longitudinally) when heated, to between one-half and one-sixth of its diameter.
Heat shrink tubing can be made of any one of a range of thermoplastics, including polyolefin, polyvinyl chloride (PVC), Viton® (for high-temp and corrosive environments), Neoprene®, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and Kynar®. In addition to these polymers, some types of special-application heat shrink can also include an adhesive lining that helps to bond the tubing to underlying cables and connectors, forming strong seals that can often be waterproof. Another material that is sometimes added to heat shrink tubing is conductive polymer thick film, which provides an electrical connection between the two or more conductive objects that are being joined by the tubing without the need to solder them first.