A Complete Guide to Heat Shrink Tubing

Heat shrink tubing is a versatile plastic layer which can be applied to cabling and components for several purposes by electricians, engineers and similar professionals, including:

• Electrical insulation - for example, to repair a damaged or exposed length of wire
• Protection – from dust, chemicals, moisture or abrasion
• Reinforcement – relieving the strain applied by cables held at tension
• Bundling multiple wires into a single unit
• Identification – the wide range of available colours allow for easy coding

They are also known as heat shrink sleeves, in particular when used with cables.

The name refers to the fact that the tubing is designed 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 the full size.

It is important when using heat shrink tubing to proceed with caution and observe basic safety measures to avoid accidents or injuries. Here’s how to use heat shrink tubing:

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 hand held heat gun or a heat shrink oven. The latter are specialist appliances for more precise and advanced heat application
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

Heat shrink tubing is available in two basic types, 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. An additional adhesive layer within the tubing provides protection against moisture.

Heat Guns

Electric heat shrink guns are the principal method of applying heat to tubing, wrap and tape. These versatile appliances are lightweight and available with both single and double handles.

Determining what size heat shrink tubing you will need begins with the diameter of the materials to be covered.

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:
   • 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
   • The thickness of the tubing walls. This is normally measured in millimetres or inches
   • The ‘inside diameter’ (ID) of the tubing following shrinkage as well as its ‘expanded inside diameter’ (expanded ID) before shrinkage. The latter measurement will be the one 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
3. Consider the length of the tubing. This will decrease somewhat when shrunk – normally between five and ten per cent - and this should be taken into account when selecting the length of tubing in order to ensure full coverage

What Size Heat Shrink Tubing Do You Need?

• 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.

Can You Cut Heat Shrink Tubing?

Yes. Standard scissors and a ruler will be adequate in most cases, unless you require an exact length of tubing, in which case use a more precise measuring tool. For thicker tubing you may require wire cutters or pliers.

Do not attempt to cut tubing lengthwise as this will affect its strength and moisture-proofing and could also encourage tearing.

Can You Use Electrical Tape Instead of Heat Shrink Tubing?

This may be possible in limited instances but electrical tape is less durable than heat shrink tubing and is also more prone to lose its adhesion over time. As a result, you may need to regularly inspect electrical tape to ensure ongoing integrity which may be impractical in some instances.

Electrical tape is quick and easy to apply but it does not offer the same level of protection against corrosion, moisture or wear, so it is not a good choice in unforgiving locations.

How Do You Remove Heat Shrink Tubing?

The first step is to locate the end of the heat shrink tubing. Then, grip this with thin pliers – needle nose pliers would be a good choice – and pull gently away from the connection. Finally, trip the tubing off using a blade while keeping the wire away from the electrical connection.

Is Heat Shrink Tubing Waterproof?

Yes, most heat shrink tubing is watertight and will also protect against other moisture and even potentially corrosive liquids.

What Temperature is Needed for Heat Shrink Tubing?

This varies according to the material used to make the heat shrink tubing. For example, polyolefin shrinks at around 90°C, while PTFE (Teflon) requires a considerably higher 250°C.