Heat shrink tubing (or commonly "heat shrink") is a tube which shrinks in iameter when heated. Its diameter and thickness can vary, and there are three main categories, thin wall, medium wall and thick wall tube. Heat shrink is used to insulate wires, connections, joints and terminals in Electrical Engineering. It can also be used to repair wires, bundle wires together, and to protect wires or small parts from minor abrasion.