A sample of heat shrink insulation is exposed to an elevated temperature and allowed to fully shrink to its reduced size (Unrestricted Shrinkage, method 5.5), after which the thickness is measured by one of the three methods presented in the standard:
- Micrometer Method – A smooth gauge rod of known diameter is used as a reference, placed in contact with a portion of the heat shrink that has been split lengthwise. A micrometer measures the thickness of the rod and insulation together, and the values are subtracted to determine the wall thickness.
- Optical Method – A calibrated microscope is used to measure the wall thickness directly.
- Alternate Method – A micrometer is used to measure the thickness at multiple points of the sample. Sufficient measurements are made to determine the minimum and maximum thickness of the sample. (Ref ASTM D2671)