Insultab has a lot of experience spotting where people go wrong when it comes to measuring heat shrink tubing. It’s actually simple when you have a common vocabulary and know the right formulas.

Here is the information you will need to get your tubing measurements right – so you get exactly what you need for your project. …or better yet, call Insultab’s Customer Service team, and they will do it for you.

One of the most important tasks is choosing the size of tubing needed for your project. Here is how it is done. First, take your tubing and lay it flat on a smooth surface. Next measure the width of the flattened tubing. Then multiply the width by 2 and divide this number by Pi (I bet you remember this one from school 3.1416) and you have your answer – this is the tubing diameter you will need for your project.

1. Determine the diameter size of the tubing.

Measure the diameter of the underlying materials to be covered – at the widest part.

Select tubing that is 20% – 30% larger than this measurement by referring to the product’s Technical Data.


2. Determine the shrink ratio of the tubing.

Heat shrinkable tubing is available in 2:1, 2.5:1 or 3:1 shrink ratios meaning the tubing has been expanded to twice, two and a half times or three times its fully recovered size. The greater the size variations of the underlying materials being covered, the larger the shrink ratio required.

For example:

  • 2:1 shrink ratio: 1/2″ will recover to 1/4″ — 50% shrinkage.
  • 3:1 shrink ratio: 3/4″ will recover to 1/4″ — 67% shrinkage.
Shrink ratio

3. Determine the wall thickness of the tubing.

Nominal Recovered Wall Thickness – The target thickness of the wall after complete recovery. The Wall Thickness of the tubing is measured in inches (in.) or millimeters (mm). Refer to the tubing’s Technical Data to determine the thickness of the wall.

Wall thickness

4. Determine the length of the tubing.

Longitudinal Shrinkage – Heat shrinkable tubing has a small loss of length during the recovery process. Take into account the change of length of the recovered tubing (after shrinking). Longitudinal shrinkage varies from 5% to approximately 15% – depending on the material. Refer to the Tubing’s Technical Data for the shrinkage information.

Length of Tubing