A Complete Guide to Heat Shrink Tubing

Heat shrink tubing is a versatile plastic layer that electricians, engineers, and similar professionals can apply to cabling and components for several purposes.

• 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 allows 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 a silicone 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:

• Choose the right size tubing with the correct shrink ratio to ensure a snug fit after shrinking. Ensure it covers the wire or components adequately across both breadth and length.
• Check the tubing's expandability to accommodate any potential size changes of the components. Follow recommended heating temperatures to prevent uneven application or melting.
• Cut a suitable length of tubing and slide it over the target components. Heat the tubing using a handheld heat gun or a heat shrink oven for precise application.
• When using a heat gun, move it back and forth across the tubing to evenly shrink it and avoid burns. Heat until the wrap is tightly secured.

Heat shrink tubing works thanks to the responsiveness of the multiple materials used to make the product. Each has different strengths and properties.

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.

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 to be covered.
2. Select tubing that is approximately 20-30% larger than the measurement taken in step one.
3. Consider the shrink ratio of the tubing (e.g., 2:1 or 3:1) and the thickness of its walls.
4. Take note of the 'inside diameter' (ID) of the tubing after shrinkage and its 'expanded inside diameter' (expanded ID) before shrinkage, typically displayed on the labelling.
5. Account for the tubing's length, which decreases by five to ten percent when shrunk, 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.