Three tips to manufacture heat shrink tubing:

1. Use the oven or other heating equipment to heat tube till a high elastic state

2.Add an applied load(such as bag inflator, vacuum adsorption) to expand it enoughly.

3. use air-cooled or water-cooled cooling the tube rapidly when it keep expansion. It fixed and finished when get a state like glass.

 

Just heat the tube then it will back to high elastic, it will shrink since no applied load effect, covering on pipe or wires tightly to protect them.