What is Longitudinal Change (Shrinkage) in Heat Shrink Tubing?

You just finished shrinking tubing over a connector in a harness, but the connector is not fully covered. Why? Is it because you didn’t factor in that when shrinking, the tubing will also shrink not just overall, but also in length?

In most cases, the shrinkage is very minimal, less than 10% of its original length. Longitudinal change, sometimes called long change, or even just shrinks back in heat shrink tubing means that you need to take the right dimensional measurements. Longitudinal shrinkage is a percent measurement of the tubing that is shortened during the recovery process.

How to Calculate Longitudinal Change

Longitudinal Change Ratio = ((L1-L2) / L2) x 100

L1 = Length after recovery
L2 = Length before recovery

To calculate your heat shrink tubing’s longitudinal shrinkage, you will want to cut a piece of tubing to length. Then measure that piece of tubing, shrink it, and measure the tubing again. Using those measurements, use the above formula to calculate the shrinkage. For longer lengths, try heating both ends of the tubing to shrink it to the material before heat shrinking the mid-section of the tubing.

Measurements are not accurate? You may want to take into account these factors:

• Is the tool that you use to measure able to calculate small changes? Remember, the shrinking may be minimal. Try another tool, or use a longer piece of tubing to calculate the changes
• Is your heat gun not shrinking the tubing? Make sure that you are heating the tubing to the correct temperature specified on the datasheets, and your heat gun is able to maintain the correct temperature
• Did you accidentally stretch the tubing out before heating? Take care that the tubing was not altered before shrinking, or stretched out over the material you are covering.

Heat shrink tubing is pliable and stretchy and changes its shape when heated. You must take that into account when determining what length tubing you will want when it is recovered, and adjust for any additional longitudinal shrinkage that may take place during the heating process.

For questions on heat shrink tubing or if you need help selecting the correct size, contact our customer service team via chat or call us at 800.633.6339 and we can get you on the right track.