Heat shrink tubing behavior: How to predict recovered (post-shrink) wall thickness

Heat shrink tubing is prized for its ability to provide a thin, flexible jacket or insulative cover for catheter-based devices without significantly adding to the device profile.

Here’s a question we hear a lot: “How do I know how thick the tubing wall will be after the tubing is applied?” To choose the right heat shrink tubing, it’s important to understand how a tubing layer would affect your overall device profile.

A good analogy is a party balloon. When the balloon is fully inflated (expanded), the wall is very thin. If you let the air out, the wall gets thicker as it deflates. (Because, conservation of mass.)

Similarly, there’s an inverse relationship between tubing inner diameter (ID) and tubing wall thickness: as the tubing shrinks, the wall gets thicker. But unlike a party balloon, our heat shrink tubing is engineered to behave consistently from lot to lot.

If you know the OD of the substrate and the ID of the heat shrink tubing, you can predict the recovered wall thickness of the tubing and determine whether it will fit the requirements of your project.

It’s important to note that the Recovered Wall Thickness listed on our data sheet is based on the Recovered ID maximum—the smallest ID possible for that tubing. However, heat shrink tubing can be partially recovered (shrunk) to achieve a range of IDs, depending on the outer diameter (OD) of your substrate.

Heat Shrink Tubing Behavior

Let’s say you have a laser-cut hypotube with an OD of 0.030” and you’re thinking of jacketing it with 72D 2:1 ratio Pebax® Heat Shrink Tubing with an expanded ID of 0.036” (shown in orange). The graph below shows that this tubing can recover (shrink) to accommodate that 0.030" hypotube, and at that size, the tubing wall thickness will be about 0.0025”. Why? Because at partial recovery, the tubing hasn’t reached its full shrinkage potential. The material “thickens” less, resulting in a thinner final wall.

This is significant because engineers often look at the Recovered Wall Thickness listed on the data sheet and assume that the tubing will be too thick or too stiff for their application—especially for flexible catheter designs. In reality, if they’re not shrinking the tubing all the way down, it ends up thinner and more flexible than they expect.

Being able to predict the recovered wall thickness of various heat shrink tubing options will help you select the right tubing ID and wall thickness for your application.

Ready to try our Pebax or Polyolefin Heat Shrink Tubing? Browse our inventory on Chamfr. If you’re not sure what tubing is best for your project, we can provide guidance that will reduce iteration cycles, save cost, and shave weeks off your timeline. Just complete this form and we’ll take it from there.