The Complete Beginner’s Guide to Heat Shrink Tubing

By: CableOrganizer®

Many pros and DIYers alike count on the trusted reliability of heat shrink tubing to add support to their wires and cables. It can serve multiple purposes, including cable management, electrical insulation, strain relief, environmental or mechanical protection, color coding, and to professionally finish braided sleeving. This handy solution can be used for a range of applications, such as for automotive, marine, aviation, military, audio, video, communications, and much more. If you would like to learn the basics for applying heat shrink, as well as other tips and facts about this solution, you’ve come to the right place.

COMMON MISTAKES HEAT SHRINK FIRST-TIMERS MAY MAKE:

People new to applying heat shrink tend to make some common errors when they are first learning how to use it. But as with everything in life, practice makes perfect. Beginners may first choose tubing that is too small or large because they are not familiar with the concept of heat shrink ratio or recommended measuring techniques. Not properly cleaning cables before an application is another novice error, such as not wiping oil, or dirt from the surface, and not addressing sharp edges that could potentially damage the tubing. Applying inadequate or excessive heat is another mistake, which can cause the heat shrink to melt, deteriorate, or shrink unevenly. Plus, beginners may not choose the correct heat shrink variety, which can cause the application to not function as it should. This may also accrue unnecessary expenses, if the proper supplies need to be purchased.

EXPLORING THE HISTORY OF HEAT SHRINK:

Before doing a deep dive into applying heat shrink, let’s learn about its origins.

Raychem Corporation invented this helpful thermoplastic tubing in the late 1950s. Scientists like Paul Cook (one of Raychem’s founders) started experimenting with radiation chemistry while at Stanford Research Institute, a technique that changed the molecular structure of polymers. The Raychem company name, in fact, was derived from the term “radiation chemistry,” with the company founded in 1957 based on these experiments.

Raychem researchers learned that crosslinking (the process of joining separate polymer molecules with chemical bonds) could create heat-recoverable products, as they experimented on thermoplastics with high-energy electron-beam irradiation and other methods. In doing so, they observed a “memory effect” in which covalent bonds linked individual polymer chains together. This phenomenon strengthened the thermoplastics, giving them greater elasticity and resistance to heat and chemicals. After irradiation, the tubing was heated, then mechanically expanded and cooled. They found that after heat was applied to the altered tubing, it returned to its original, pre-expanded diameter.

OTHER METHODS FOR ACHIEVING HEAT SHRINK MEMORY

Not every heat shrink variety develops memory from the usual crosslinking method. Irradiation can deteriorate high-performance polymers like PTFE (Teflon®) because of its physical structure, with radiation-thermal modification the preferred technique. PTFE is first heated within an oxygen-free vacuum beyond the melting point of 621°F (327°C), then blasted with ionizing radiation to crosslink it. It is next expanded while it is hot and highly elastic, to several times its original diameter. Instant chilling with cold water causes its tense chains to freeze into rigid crystals. Once PTFE tubing is heated, the crystals melt and snap back into their original shape.

Like PTFE, polyvinyl chloride (PVC) may also be produced using molecular orientation techniques. In this process, a polymer is heated above its glass transition temperature and then mechanically stretched, which causes polymer chains to align. Plastic memory is created from rapidly cooling the PVC tubing, which causes mechanical tension in the material, enabling it to later shrink when reheated.

WHAT ARE SOME OF THE STANDARD HEAT SHRINK MATERIALS?

There are several types of materials often used to make heat shrink tubing. Polyolefin, one of the most familiar, is frequently chosen for its wire bundling and electrical insulation capabilities. Some polyolefin tubing is enhanced with a glossy finish for aesthetics. When a dual wall adhesive lining is included within polyolefin sleeving, it melts after heating to form a weather-tight seal. Polyolefin can be paired with a dual wall inner layer conductive cloth for electromagnetic (EMI) shielding. Some polyolefin heat shrink can be made with self-extinguishing components to resist diesel, oils, and aviation fuels. An outer layer of polyester yarns is combined with an inner layer of polyolefin tubing to create fabric heat shrink that protects against abrasion, chafing, and cutting.

Higher temperature applications call for heat shrink made from heat-resistant materials like Viton®. This rubber-like fluoroelastomer is extraordinarily resistant to fluids, solvents, and flames. In demanding mechanical environments, Kynar® heat shrink is often chosen for its resistance to chemicals, flames, and abrasion.

FACTORS FOR CHOOSING HEAT SHRINK MATERIALS:

Different factors or environments may influence your choice of heat shrink. They may include:

Mechanical Wear: Heat shrink can overall safeguard your applications against mechanical wear, such as from abrasion and vibration, as well as provide strain relief. Dual wall heat shrink adds reinforcement with its adhesive lining, providing rigidity to the application.

Heat Exposure: When your environment is subject to high heat, such as in an engine or within industrial equipment, you need to choose heat shrink that can stand up to higher-heat limits, like PTFE, Kynar®, Viton®, or polyolefin with diesel resistance. Spec sheets for the heat shrink product you choose will help you make the best choice for your application, detailing minimum shrink temperatures, the continuous operating temperature range, and whether the heat shrink is flame retardant.

Moisture: It is always a good idea to choose heat shrink with resistance to water, when you have environments with heavier moisture. This is where adhesive-lined heat shrink is beneficial, and forms a bond where moisture, humidity, and corrosion are an issue. Heavy wall heat shrink can be used in direct burial applications, as well as those that require protection in harsh environments.

Chemicals: When you need to keep your applications safe from chemicals, oils, and harsh fluids like fuels, this is also an appropriate environment for PTFE, Kynar®, Viton®, or diesel resistant heat shrink. Neoprene heat shrink provides excellent fluid and solvent resistance.

WHAT IS SHRINK RATIO?

Shrink ratio describes how much a heat shrink tubing's diameter can reduce after heating. The ratio’s first number represents the tubing’s original expanded diameter and the second number, its size after shrinking. The greater the first number, the more you can expect the heat shrink tubing to shrink.

Heat shrink tubing that shrinks to half of its original diameter is known as a 2:1 ratio. This size is often used for standard wire and cable applications, as well as for inner splices.

If your wiring project has a tricky fit, 2.5:1 heat shrink tubing can come to the rescue. It is a viable choice for repairing frayed cable ends, sealing automotive wiring, organizing home theater cords, or when upgrading electronics.

A 3:1 shrink ratio reduces to one-third of its original diameter. This is perfect in cases where a much smaller wire is paired with a larger connector. When this size comes with a dual wall adhesive lining, it tends to provide some basic waterproofing.

Irregular applications and applications where components have drastic size differences are great candidates for the 4:1 shrink ratio. It shrinks to one-quarter of its original diameter. This size can be appropriate for heavy duty environmental sealing, and superior mechanical protection when harnesses are subject to bending, pulling, and abrasion.

The 6:1 ratio is typically a good match for applications with significant diameter differences between a cable and connectors, or other components. This shrink ratio is often used in automotive repair, heavy equipment, and marine wiring. It contracts to one-sixth of its original expanded size and is often paired with a dual wall adhesive inner lining for maximized strain relief and waterproofing.

Now that you’ve learned about heat shrink tubing, it’s time to get started on your projects. Shop for heat shrink tubing, braided sleeving, heating and termination tools, and more at CableOrganizer® now.