What is heat shrink tubing?
Heat shrink tubing (also known as heat shrinking) is the process of encasing wires or cables in plastic tubes that shrink when heated to form a close-fitting casing. There are a number of benefits to heat shrinking.
Here are four key advantages:
1. Protect wires and cables
The key benefit of heat shrinking is the protection it offers to cables and wires. The tubing protects the cables from abrasion in moving parts and areas that see a lot of use. Additionally, the tubing protects cables and wires from environmental effects that could otherwise damage them, including liquids like oil, water and acids and also atmospheric factors, such as humidity, and temperature.
2. Insulation
Heat shrink tubing sizes vary, ensuring the perfect fit for cables and wires. This fit means that in most cases, it performs better than basic insulation products. It’s also more reliable due to the tight fit that it provides – it won’t come off with age, in contrast with other insulation solutions.
3. Relieves strain on wires and cables
Cables and wires are often stretched or put under strain due to insufficient length or being squeezed into confined spaces. This can adversely affect the lifespan of cable and wiring. Heat shrinking cables can reduce the strain to keep them in tip-top shape.
4. Bundling Cables together
Due to the variety in heat shrink sizing, it’s possible to group cables and wires together in a single tube. Not only is this better from an aesthetic point of view, but it’s an extremely effective cable management technique.
Heat shrink tubing material
The most popular material for heat shrink tubing is polyolefin, which is especially favoured by the military, aerospace, electronics and railway industries. This should give you an idea of its durability. Polyolefin’s advantage derives from the cross-linking polymer chains.
Polyolefin
| Standard application | Insulation, mechanical protection and marking |
| Features |
|
| Shrink ratio High-grade shrink ratio |
2:1 3:1 |
| Shrink temperature | 100°C (212°F) transparent, 3" and 4" > 100°C (212°F) |
| Maximum continuous-use temperatures | -55 to 135°C (-67 to 275°F) |
Why colour code?
Tubing can be colour coded to enable engineers to quickly and safely determine the function of cables, avoiding the dreaded cable spaghetti. This helps repairs and system management to be conducted efficiently and makes your cable and wiring appear organised and professional.
What is adhesive-lined polyolefin heat shrink tubing material?
Adhesive-lined polyolefin heat shrink tubing is a specialty solution. It’s a standard polyolefin tube with an inner-liner of adhesive that melts and flows at the same temperature at which the polyolefin tubing shrinks. When heat is applied, the tubing shrinks. The adhesive flowing fills the voids and conforms to the underlying shape to form a seal. The seal protects the interior components from moisture, debris and other contaminants.
- Typical applications: Wire harnesses and splices that need insulation and sealing in the automotive industry. Also popular with the marine sector.
Heat shrink size
You need to know these terms to determine your heat shrink sizing, which appear on technical data sheets:
Inside, or Inner, Diameter (I.D.) Supplied
This is the minimum I.D. of the tubing – before it’s heated – as it was supplied by the manufacturer.
Recovered Inside, or Inner, Diameter (Recovered I.D.)
When heat is applied to expanded tubing, the tubing shrinks, or recovers. The Recovered I.D. is the measurement of the tubing’s Inside Diameter after it shrinks back to its original extruded size.
The diagram shows you the information you’re looking for to get the right shrink tube sizes.
Determining the correct shrink tubing sizes
You’ll need to collect some information first.
Step 1: What’s the diameter of the tubing?
Measure the widest diameter of the materials that your expanded sleeve will slide over.
- When selecting your tubing, look at the technical sheet. You should allow an additional 20—30% allowance on your supplied I.D., which will provide enough space for the heat shrink tubing to fit over any protrusions.
Step 2: What’s the shrink ratio?
Heat shrink tubing comes in different shrink ratios, such as:
- 2:1
- 2.5:1
- 3:1
This tells you that the tubing has been expanded twice, two-and-a-half times or three times it’s full recovered size. The bigger the size variations of the underlying materials that you’re covering, the larger the shrink ratio you’ll need.
Example: 3:1 shrink ratio: 3/4" will recover to 1/4" — 67% shrinkage
You should know:
- A high shrinkage ratio indicates that the tubing is more suitable for connectors. This is because as it can encase the connector body and still shrink to cover a wire or cable.
- In general: the tubing’s supplied I.D. and the size of the object you’re protecting should NOT exceed a 40% ratio, in order to allow effective coverage.
Step 3: What’s the length of the tubing?
During the recovery process, the tubing will experience a small loss of length, which you’ll need to account for. Shrinkage can vary, anywhere from between 5—15%. Here again, the technical data should be able to supply you with that information.
Step 4: What’s the wall thickness?
When anything stretches, it thins out. The more stretched, the thinner it gets. In heat shrink tubing, the opposite also occurs. The more it shrinks, the thicker it gets. If it’s not allowed to return to its specified Recover I.D., then it won’t recover to its specified thickness either. You’ll find it too thin. If wall thickness is an issue for you, then take note.
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Questions?
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