Expand Heat Shrink Tubing

This article will show you how to expand electrical-insulating heat shrink tubing by stretching it.

Steps

Select the right tool for the size of the heat shrink tubing you want to expand.

Most smaller tubing is easy to stretch with needle-nose pliers. If possible, find a pair with extended ends to accommodate longer sections of tubing.
To stretch larger tubing, use a combination of two pliers to expand the tubing as shown in this illustration.
- Extremely small tubing calls for tweezers with needlepoint tips, such as LTD's Tweezerman models.
Insert the tweezers or pliers into the tubing as far as possible. Make sure the tool used is completely closed.
Pull the pliers apart slowly to open up the ends. If using tweezers, use a jeweler's screwdriver to help pry the tweezers apart.
Stretch the tubing only a little at a time to avoid tearing or puncturing it.
Close the tweezers or pliers and rotate the tubing slightly.
Repeat steps 2 through 5 until you have rotated the tubing enough to return to your starting point.
Flip the tubing to so that the other end of it fits over the tweezers or pliers, and repeat the above steps.
The tubing is now ready for use.

Stretched/expanded tubing will shrink much faster, using less heat, than an equivalent piece of tubing that has not been stretched.
Use the following for determining safe dielectric withstanding voltages when expanding heat shrink tubing: For every mil (1/1000 of an inch) in thickness, typical Polyolefin heat shrink tubing (MIL-DTL-23053/5, Class 1 and 3 specification), with a standard wall thickness tolerance of ± 20%, will have a dielectric withstanding voltage of 500 volts. The smallest available heat shrink tubing has a thickness of 0.2 mil, even though most sizes are around 1 mil. For the smallest heat shrink tubing, expanding it to double its size may reduce its thickness by up to 50%, which is 0.1 mil. Multiple this by its withstanding voltage of 500V/mil, and the smallest heat-shrink tubing will still withstand 50V. However, when the tubing is heat-shrunk, its thickness will increase, which will in turn increase its overall dielectric withstanding voltage.
Good-quality tubing can expand to more than twice its size. Stretching as described above should not puncture or tear it.

Be gentle with delicate tweezers. Using any metal object to pry them apart, as in the illustrations above, can damage them.
Expanding any tubing beyond its original size changes its thickness and may affects its dielectric withstanding voltage. If your project or application of expanded tubing is already within close tolerances, test an expanded section of tubing first, in a safe, controlled environment.
Be careful when cutting off sections of the sleeving. If the cut is uneven or jagged, that will make the tubing more susceptible to tearing when stretched.