Step 1: Understand Your Application
The most important aspect of choosing the right heat shrink tubing product for your needs is to understand and define all that is necessary for your application. The only way to ensure that you’re getting the most appropriate and cost-effective product is to fully understand your application and the requirements that you need to meet.
Regardless of whether you’re using heat shrink tubing in an electrical application, as a strain relief, as a protective covering, or for any other reason, determining the correct size is the most important factor.
A great start point is to measure the 2 most important dimensions:
- The largest diameter that the expanded sleeve needs to slide over
- The smallest diameter that the tubing needs to completely cover to (after shrinking).
These two dimensions will be used later in Step 2 to help you determine the required size and shrink ratio for your tubing.
Another important dimension to consider is the wall thickness. A certain minimum wall thickness might be required due to the electrical requirements of your application. Or, if the tubing is going to be subjected to excessive abrasion or wear, you may wish to have a heavier wall thickness than the standard size offers. In addition to defining your required minimum wall thickness, it is also necessary to determine the diameter at which this wall thickness will be required. This information is critical in choosing the required tubing size in Step 2.
Electrical Property Requirements
If your heat shrink tubing is going to provide electrical insulation or bundle electrical wires, it is likely that it needs to meet certain regulatory guidelines. In order to choose the correct product for your application, you’ll need to know if any specifications need to be met. In the heat shrink world, the most common ones are listed below
- UL (Underwriters Laboratories)
- CSA (Canadian Standards Association)
- ASTM (American Society for Testing and Materials)
- AMS (Aerospace Material Specification)
- EU (European Union)
- RoHS (Restriction of Hazardous Substances Directive)
- VDE (Verband der Elektrotechnik)
There are literally hundreds of industry or application based specs that you may need to consider, automotive or military specifications are very common and can differ greatly from one manufacturer to another, but regardless of the origin, these specifications all tend to be in place to cover common electrical requirements such as dielectric strength and flame resistance.
Other possible electrical requirements could be that the tubing must be free of halogens or that it must be made out of a specific material. Make sure you understand all of the electrical requirements before you choose your heat shrink product.
Another critical step in defining the requirements of your heat shrink tubing application is to understand the environment in which the tubing will operate. For example:
- Will the tubing be subjected to excessive abrasion or flexing?
- Will the tubing come into contact with any oils, greases, fuels, chemicals, or other fluids?
- Will be used indoors or outdoors?
- If it is going to be used outdoors it could be subjected to excessive UV exposure.
- If it is going to be lying on or buried below the ground, it may need to have superior resistance to fungus growth.
- Does the application require an enhanced environmental seal (as obtained with adhesive-lined heat shrink tubing)?
- Will the tubing need to protect any sensitive portion of the object the tubing is covering?
All of these factors and more will need to be considered prior to selecting your heat shrink product.
Step 2: Determine the Required Tubing Size
The next step is to determine the most appropriate tubing size for your application. Using the measurements you obtained in Step 1, you’ll need to define the following tubing dimensions that best suit your needs:
- Minimum expanded ID
- Maximum recovered ID
- Minimum recovered wall thickness.
This section will explain each of these tubing dimensions and how they relate to your application measurements found in Step 1.
Expanded and Recovered Inside Diameters
Heat shrink tubing is traditionally specified by the minimum original inside (“expanded”) diameter and the nominal shrink ratio. However, a good heat shrink product datasheet will not only list the minimum expanded ID and nominal shrink ratio of the tubing, but also its maximum recovered ID.
First, check that the minimum expanded ID of the tubing is greater than the largest diameter that the sleeve needs to slide over (using the measurement you made in Step 1). Then, check that the maximum recovered ID of the tubing is less than the smallest diameter that needs to be completely covered (also measured in Step 1).
The diagram below illustrates these tubing dimensions:
If the product datasheet does not have maximum recovered ID listed, you can estimate it using the minimum expanded ID and the shrink ratio.
If a heat shrink product has a 2:1 shrink ratio and the minimum expanded ID is 6.4mm, then the maximum recovered ID should be 3.2mm
6.4mm ÷ 2 = 3.2mm.
If a heat shrink product has a 3:1 shrink ratio and the minimum expanded ID is 39.0mm, then the maximum recovered ID should be 13.0mm
39.0mm ÷ 3 = 13.0mm.
Now that you have determined the required expanded and recovered ID’s (and also the shrink ratio), you may need to consider the wall thickness required for your application.
The wall thickness of a heat shrink product is traditionally specified as the minimum thickness at the fully recovered stage. If the diameter of what you are covering is greater than the maximum fully recovered diameter of the tubing, the final wall thickness will be less than what is specified on the datasheet. This is illustrated below:
The dimension trec is the wall thickness of the tubing when allowed to shrink fully without restraint. However, since your object is restraining the tubing from shrinking fully, you’ll need to determine the required tact before you can specify the tubing. The approximate relationship between the two thickness dimensions is as follows:
t rec = (d obj x t act) ÷ d rec
t act = (d rec x t rec) ÷ d obj
t act = actual wall thickness after shrinking onto the underlying object
d obj = diameter of the underlying object
t rec = specified recovered wall thickness of tubing
d rec = specified recovered diameter of the tubing
Length & Longitudinal Shrinkage
If tubing length is a critical dimension for your application, longitudinal shrinkage must be considered. In addition to shrinking in diameter, most heat shrink tubing products will also shrink in length. This is particularly important when using cut pieces or you have a specific length that you need to cover.
The amount of long shrink you can expect depends largely upon the shrink ratio and the manufacturing processing variables, but it is generally about 5%-10% of the original length.
Step 3: Choose the Appropriate Heat Shrink Material
So, you now understand your application and have chosen the appropriate size tubing. You are now ready to choose your heat shrink material. Often there are multiple products that will meet your needs, so it is important to also know the cost and availability of each option. This section will examine how to choose the right
Often there are multiple products that will meet your needs, so it is important to also know the cost and availability of each option. This section will examine how to choose the right material.
Polyolefin is the most widely used material for manufacturing heat shrink tubing, but there are many other speciality heat shrink tubings available in various fluoropolymers and elastomeric materials along with commercial options such as PVC.
Within each of these material families, there are many different compounds that have been designed to excel in certain environments and/or meet particular specifications.
Polyolefin Heat Shrink Tubings
Polyolefin is used widely as the base material for standard heat shrink tubing products, when this material is combined with other compounds, it is possible to produce bespoke materials that perform in certain ways:
- LTF100-V – Low-cost heat shrink tubing
- LTF100 – Low shrink temperature tubing
- PLF100 – Military Grade heat shrink
- PLZH100 – Zero Halogen heat shrink
- PLF103 – 3:1 High shrink ratio tubing
- SEC150 – Transparent Flame retardant
Adhesive-Lined Heat Shrink Tubings
Adhesive lined (or “dual wall”) polyolefin heat shrink tubing is a speciality product that has a wide variety of uses. This product is simply a standard polyolefin tube that has an inner-liner of adhesive that melts and flows at the same temperature at which the polyolefin tubing shrinks.
As heat is applied and the tubing is shrinking, the flowing adhesive fills voids and conforms to the underlying shape. This forms an environmental seal, protecting the underlying component(s) from moisture or other contaminants. An example of the use of adhesive-lined tubing is shown in the photo below:
Other Heat Shrink Materials
In addition to the products mentioned above, there are also other specialty heat shrink products available. These products all offer unique qualities such as extreme temperature resistance, exceptional chemical/fluid compatibility, and/or superior mechanical properties. Among theses products are:
Due to the enhanced qualities of these products, they are generally more costly than Polyolefin tubings. In some cases, the price differences are extreme. The diagram below gives you a simple, generic comparison of the price differences for a sampling of heat shrink materials:
Step 4: How to Use Heat Shrink Tubing
For a full, in depth explanation of how to install heat shrink tubing, please read our article on how to install heat shrink tubing as it discusses various heating methods commonly used to shrink heat shrink tubing.