Heat shrink tubing is used in many applications by many industries. It starts as a larger tube, which shrinks to fit around the different wire and cable components once the heat is applied. It is easy to handle, simple to use, and quick to install. However, with all of the different sizing and performance requirements involved in choosing the correct heat shrink tubing product, it can seem intimidating.

For heat shrink tubing success, you must understand the tubing’s application, how to take the proper measurements, how to differentiate between the materials available, and how to properly install the tubing. This basic guide to heat shrink will cover it all.

Common Uses for Heat Shrink Tubing

Heat shrink tubing is a versatile product that can be used in a wide range of applications. These are some of the most common purposes for heat shrink:

• Mechanical Protection— Tubing defends against external threats such as abrasion, cut-through, denting, and more.
• Environmental Protection— Shrink tubing creates a seal around components to keep out moisture and chemicals that could otherwise damage the wire.
• Electrical Insulation— It can be used to cover terminals, splices, connectors, and wire repairs.
• Identification— It is available in a spectrum of colors and can be used for color-coding or component identification. Several types of heat shrink, including PVC tubing, can be custom printed to make identification simple. Click here to learn more about value-added identification services.
• Strain Relief— Tubing can take the pressure off other wire and cable components.
• Wire Bundling— Heat Shrink is commonly used in wire harnesses, organizing wires for more convenient handling and installation.

Application Considerations

To find tubing that will last in its application, you must consider all required performance characteristics and industry specifications. You must also take into account any environmental conditions the tubing will have to withstand.

• Electrical Requirements— Like most wire and cable products, there are many industry standards that apply to heat shrink tubing. If the heat shrink tubing is used to bundle or insulate electrical wires, it will probably have to meet guidelines set by standards organizations such as UL, CSA, or ASTM. Depending on the application, the tubing may also be required to meet specific automotive, aerospace, or military specifications. Click here to learn more about wire and cable standards.
• Environmental Requirements— Will the cable be used indoors or outdoors? Will it be exposed to water, chemicals, crushing, or other types of physical harm? Consider all of the challenges the tubing will face in its application to ensure that a sufficiently durable heat shrink tubing option is chosen.

Important Measurements

Although measuring for heat shrink tubing is relatively simple in practice, it can be daunting for beginners. You may see a number of different measurements on spec sheets that seem unfamiliar. You may not even know how they correlate to the tubing itself or to the parts you are trying to cover. Here, we will break it all down. These are the main points you must consider when determining heat shrink tubing size:

• Sizing Requirements for Application— Take careful measurements of the largest and smallest parts the tubing must cover. To calculate the diameter of a part that is not circular, simply measure the perimeter of the object and divide by pi (3.14). While it isn’t exact, it will give an approximate number to reference when searching spec sheets for an appropriate tubing diameter.
• Expanded and Recovered Inside Diameters— The expanded inside diameter (expanded ID) refers to the diameter inside the tubing before it is heat-shrunk. The recovered inside diameter (recovered ID) references the diameter inside the tube once it is in its shrunken form. With these measurements, be sure that the minimum expanded ID is larger than the largest part that must be covered, and that the maximum recovered ID is smaller than the smallest part to be covered. Checking these measurements will ensure that the tubing is large enough to fit over wide or irregular parts while shrinking enough to create a snug fit over small parts.
• Shrink Ratio— Look to the shrink ratio for more information on the difference between the expanded and recovered IDs of the tubing. If the tubing has a shrink ratio of 3:1, the expanded tubing will be three times larger than its shrunken form. Or, to look at it from another angle, the shrunken tubing will be one-third of the size of the original, expanded tubing. Understanding the shrink ratio will help you to determine either the expanded or the recovered ID if only one of the measurements is given on a spec sheet.
• Wall Thickness— This measurement traditionally refers to the minimum wall thickness once the tubing is fully shrunken (in its fully recovered state). This measurement, as listed on the spec sheet, does not account for an object preventing the full shrinkage of the tubing. Therefore, if the object you are covering is larger than the recovered diameter of the tubing, the final wall will actually be thinner than the wall thickness listed on the spec sheet.
• Length and Longitudinal Shrinkage— When heat is applied, the tubing may shrink longitudinally, in addition to shrinking in diameter. While this shrinkage is usually less than 15%, you should account for the potential loss by ordering extra length. Ask your supplier for more information on longitudinal shrinkage as it varies depending on the characteristics of the tubing.

Heat Shrink Tubing Materials

Although some users believe that all heat shrink tubing is the same, it is actually available in a variety of different materials to meet the needs of different applications and environments.

• PVC vs. Polyolefin— Polyolefin and PVC are two common materials used for heat shrink tubing.PVC tubing may only be used for applications with operating temperatures less than 105°C (221°F). Some of PVC’s benefits include low cost, good tensile strength and abrasion resistance, and color quality. However, Polyolefin is the most popular heat shrink material. It is a durable material that can withstand much higher temperatures than PVC tubing, in the range of 125°C to 135°C (257°F to 275°F). Because of its higher temperature resistance, polyolefin tubing is also free of any shelf-life concerns and should last perfectly until it is needed.
• Adhesive-Lined Heat Shrink— This is also called ‘dual wall’ polyolefin tubing. Adhesive-lined heat shrink features an inner layer of adhesive which melts when the heat is applied to the shrink tubing. It then molds around the object to create a seal against environmental hazards.
• Specialty Heat Shrink Products— For challenging applications, heat shrink tubing may be made with fluoropolymers such as PTFE and FEP, or with PVDF, Neoprene, Kynar, Mylar, or Viton. Although these materials are much more expensive than PVC or polyolefin, they are only necessary for applications requiring exceptional resistances or extremely high-temperature performance.

Handling and Installation Considerations

• Storage— Because PVC heat shrink does not have the high-temperature resistance of polyolefin tubing, it must be kept out of the sun and stored at temperatures below 32°C (90°F) to prevent premature shrinkage.
• Heating— Hand-held heat guns are the most common tool used for heat shrinking. However, flow-through ovens are also used, though generally for more extensive applications. The focused light is another method, but it is only used rarely. To shrink PVC tubing, it is recommended that the tubing be exposed to 150°C (300°F) heat for three minutes. Polyolefin tubing has the same recommendations, but because it can withstand higher temperatures, there is more room for adjustment in the temperature and duration.
• Minimizing Longitudinal Shrinkage During Install— If you are concerned about limiting longitudinal shrinkage, simply apply heat to the ends of the tubing first, before proceeding to the middle section.

From application considerations to measurements, materials, and handling and installation tips, you should now have a great basic understanding of heat shrink tubing. To view heat shrink tubing options available from Allied Wire and Cable, visit our online catalog.