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What Is Heat Shrink Tubing?
What is heat shrink tubing? In its most basic form, it’s a piece of tubing made of a plastic material. When you heat it, it shrinks. It’s commonly used on wiring for insulation and strain relief of electrical joints, but there are many more uses, from the cables inside your computer to a hospital’s operating theatre to equipment in outer space.
History
Heat shrink has been around a long time. Some of the plastics used in the manufacturing process were developed in the 1950s. And then, in the 1960s, the Raychem Corporation pioneered heat shrink product development.
That product development continued over the following decades and on into this century. Now we have a wide range of products designed for an equally wide range of uses.
Manufacturing Process
There are four basic steps to creating heat shrink. The first three are in the manufacturing process to make the heat shrink. The fourth step is when you, the user, heats it up and shrinks it.
Let’s get into the detail…
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- The raw materials are selected, based on their properties. Depending on the application, other materials are added, such as colorants and stabilizers. For example some heat shrink tubing might need to be provided in yellow and green stripes. Another may require an inner layer of heat-activated adhesive to seal against moisture. With the raw materials combined as needed, a tube is extruded.
- The extruded tube goes through a process of cross linking which creates a memory within the tube.
- The tube is heated up to just above the melting point of the polymer and the diameter is expanded then the tube is cooled rapidly. A vacuum chamber is often used for this step.
At this point the heat shrink is ready to be packaged, stored and sold to you, the end user perhaps via a distributor. - Using your heat gun, you heat the tube again to just above the melting point*, but this time it shrinks. In fact it will try to shrink back to the size it memorised in step 2. Hopefully you’ve chosen the correct size and it shrinks tightly onto the cable or component. If it shrinks as much as it can but still moves about on the cable then the wrong size heat shrink was used.
* Please note, when we say just above the melting point, we mean the point at which the tubing starts to soften and change shape.
Step 2 mentions cross linking. This tends to be a radiation process that changes the chemical structure, increases molecular mass and improves the materials’ properties. For example it can increase tensile and mechanical strength, abrasion and chemical resistance. (If you are into popular movies, this might be sounding somewhat familiar, but it doesn’t turn the tubing green, nor does it affect overall size).
Some FAQs
We’ve curated a list of the common questions related to heat shrink tubing that people often ask:
What is heat shrink tubing used for? What’s the purpose?
Heat shrink tubing is manufactured in different materials for different uses. Here are a few (remember that the material appropriate for one use might not be right for another use):
- Electrical insulation of a cable joint (soldered, crimped etc)
- Electrical insulation of bare wires
- Fuel/harsh chemical insulation for components and wires
- Strain relief
- Cable tidying/cable harnessing
- Cable labelling (via printed/coloured sleeves)
- Insulation against high temperatures
- Medical tools and equipment
- Utility systems (high voltage cables etc)
- Environment protection against moisture or dust
What is heat shrink tubing made of?
All our heat shrink tubing is made of plastic materials that have been pre-stretched, ready for you to heat and shrink back to the size you need. We use different materials for different uses. For example:
- Polyolefin is used for general purpose heat shrink
- Polyolefin plus an inner line of thermoplastic adhesive for dual-wall/adhesive-lined heat shrink
- Crosslinked elastomer for fuel-resistant heat shrink
- Ultra thin wall fluoropolymer heat shrink for electrical insulation in medical tools
- Kynar™ (a vinylidene fluoride thermoplastic polymer) heat shrink for use in high temperature environments
Please see our separate article for more details on what heat shrink is made of.
What is a heat shrink sleeve?
Sleeve, sleeving, tube, tubing – just different words for the same thing.
What is heat shrinking?
It’s the process of using a heat tool such as a heat gun to shrink a length of tubing onto a component or cable or other item (known as a substrate). Many people are surprised to learn that the tubing is pre-stretched in the manufacturing process and that the act of heating it causes it to shrink back to its original size.
