Dual wall heat shrink tube is made of the high quality polymer (outer layer) with hot melt adhesive ( inner layer ).The heat shrink tubing protects against moisture and corrosive environments, while providing electrical insulation and mechanical protection. During installation, the industrial adhesive lining in the heat shrink tubing melts and distributes across the lined area creating a protective, water-resistant barrier. When it cools down, inner layer forms an adhesion layer between the tubing and the component or wire. Provides a water-tight seal and protection for the connectors or wires. The continuous operating temperature is suitable for Minus 55°C to 125°C. There is also a military-standard grade with a maximum working temperature of 135°C. Both 3:1 and 4:1 shrink ratio are fine.