A Complete Guide to Heat Shrink Tubing

Heat shrink tubing is a flexible, shrinkable plastic tube designed to insulate, protect, and reinforce wires, cables, and other components. They are also known as heat shrink sleeves, in particular when used with cables. This is because the tubing is used to shrink into place and become rigid when heat is applied, providing a durable, protective coating.

Given the range of possible uses, heat shrink tubing is available in a variety of materials, sizes and colours. Some also come with an adhesive liner to help the tubing stay in place once applied.

Watch out for the ‘shrink ratio’ – the relationship between the original size of the heat shrink tube and its shrunken form following application. This is usually either 2:1 or 3:1, with higher numbers indicating a greater ratio and, therefore, a tighter fit. For example, tubing with a 2:1 ratio will shrink to half its size, and a 3:1 ratio indicates shrinkage to one-third of the full size.

A heat shrink tube is used in various ways including:

• Electrical Insulation - Heat shrink tubing is commonly used to repair damaged or exposed wires, prevent electrical shorts, and improve safety. A tight seal around conductors provides an extra layer of insulation that enhances durability and reliability.
• Protection - They can be used to shield wires, cables, and components from moisture, dust, chemicals, and abrasion. It acts as a protective barrier that helps extend the lifespan of electrical connections, especially in harsh environments.
• Reinforcement & Strain Relief - In applications where cables are under constant tension or movement, heat shrink tubing helps reinforce and relieve mechanical strain. Providing additional support at connection points and terminations prevents premature wear, fraying, or breakage.
• Wire Bundling & Organisation - Heat shrink tubing is an effective way to bundle multiple wires into a single unit, reducing clutter and improving cable management.
• Identification & Colour Coding - Available in a wide range of colours and sizes, heat shrink tubing is used for labelling and organising wires and components. Colour coding simplifies wire identification, troubleshooting, and maintenance, reducing the risk of errors in complex wiring systems.

Heat shrink tubing is made from thermoplastic materials, which contract when exposed to heat. The tubing is manufactured in an expanded form and retains this shape until heat is applied. Once heated, it shrinks to fit tightly around the wire or component, forming a protective seal.

To ensure a safe and effective application of heat shrink tubing, this is how you should use them:

1. Begin by choosing the right size tubing with the correct shrink ratio. It should comfortably cover the wire or components before it has been shrunk into place to ensure a tight fit afterwards. Remember that it will be across both its breadth and its length.
2. If the components to be covered could change size after application, ensure that the tubing has sufficient expandability by comparing its diameter when shrunk (called the ‘recovered’ diameter) with its size before shrinking (called the ‘expanded’ diameter). Check the recommended heating temperature for the tube to avoid uneven application or melts.
3. Cut a suitable length of tubing using standard scissors and lay or slide this over the target components. It’s now time to heat the shrink wrap. This can be done with a handheld heat gun or a heat shrink oven. The latter are specialist appliances for more precise and advanced heat applications.
4. If you use a gun, move the heat back and forth across the tubing and avoid staying in one place to minimise the risk of burns. Continue until the wrap has been tightly secured.

There are two basic types of heat shrink tubing in New Zealand, single or dual wall, also known as thin or double wall.

Single or thin wall tubing is reliable and physically robust. It is a good choice when electrical insulation or protection against abrasion and strain is required.

By contrast, double or dual wall tubing is a better choice in situations where protection from corrosion or a firm seal is the primary aim. It comes with an additional adhesive layer within the tubing, which provides protection against moisture.

Determining what size heat shrink tubing you will need begins with the diameter of the materials to be covered. This is what you should do on when choosing the right size for your application:

1. Measure the widest part of the cabling or components you plan to apply the tubing to.
2. Select tubing that is approximately 20-30% larger than the measurement taken in step one. To choose the right tubing, you will need to know:
3. Its shrink ratio. As mentioned above, a 2:1 ratio indicates that the tubing will shrink to approximately half its size when heat is applied, while a 3:1 ratio means that it will shrink to one-third its full size.
4. The thickness of the tubing walls. This is normally measured in millimetres or inches.
5. The ‘inside diameter’ (ID) of the tubing following shrinkage and its ‘expanded inside diameter’ (expanded ID) before shrinkage. The latter measurement will be displayed on the labelling. A variation of this – the ‘lay flat width’ – will also sometimes need to be considered. This is simply the width of the tubing when laid flat.
6. Consider the length of the tubing, as this will decrease somewhat when shrunk – normally between 5% and 10%. This should be taken into account when selecting the length of tubing in order to ensure full coverage.

Recommended Common Size of Heat Shrink Tubing

These are some of our recommendations on how to use common heat shrink tube sizes available in New Zealand:

• 5mm tubing with a .198 inch diameter is the recommended heat shrink tubing size for 12 gauge wire.
• The recommended heat shrink tubing size for 14 gauge wire is the same as that for 12 - 5mm, with a .198 inch diameter.
• For 16 gauge wire, 3mm heat shrink tubing with a 2:1 shrink ratio and a .118 inch diameter is recommended.

The recommended heat shrink tubing size for 18 gauge wire is the same as that for 16 gauge wire: 3mm with a 2:1 shrink ratio and a .118 inch diameter.

These are the principle standards and certificates for heat shrink tubing:

• UL224-2010: UL224-2010 specifies requirements for round insulating tubing made from polymers with heat-setting, heat-responsive and elastic properties.
• SAE AS23053: SAE AS23053 sets out requirements for electrical insulating sleeving that will shrink to a predetermined size when heat is applied.
• ASTM D 2671: ASTM D 2671 specifies standard methods of testing heat shrink tubing intended for use with electrical cabling.
• ASTM D3150: ASTM D3150 is a specification that applies to heat shrink made from PVC when used for electrical insulation.

There are various types and brands of heat shrink tubing available in New Zealand. When choosing the type of heat shrink tubing for your application, consider these factors:

Material - The material of the heat shrink tubing determines its temperature resistance, flexibility, and chemical durability. For instance, polyolefin is a popular choice for general-purpose applications, while PTFE and FEP offer superior heat and chemical resistance for industrial and aerospace applications. Selecting the right material ensures the tubing can withstand environmental factors such as moisture, UV exposure, and corrosive chemicals.

Shrink Ratio - The shrink ratio refers to how much the tubing will contract when heated, typically ranging from 1:2:1 to 6:1. Ensuring the tubing shrinks adequately without excessive stretching prevents gaps, weak spots, or insulation failures.

Wall Thickness - Heat shrink tubing comes in thin-wall, medium-wall, and thick-wall variants, each offering different levels of protection and durability. Thin-wall tubing is flexible and suitable for lightweight applications, while thick-wall tubing provides extra mechanical strength for harsh environments. Choosing the right wall thickness ensures sufficient insulation and resistance to abrasion, impact, and environmental stress.

Operating Temperature - Every heat shrink tubing material has a specific operating temperature range, which must align with your application’s thermal conditions. Using tubing with a lower heat tolerance than required can lead to premature degradation, melting, or cracking. For high-temperature environments, materials like PTFE, FEP, and Viton are preferred due to their superior heat resistance.