A: Heat shrinkable tubing, or heat shrink, is typically available in a ratio between 2:1 and 4:1, meaning the tubing has been expanded to twice or four times its fully recoverable size, respectively. Once heat is applied, tubing will contract tightly around all interior components. When choosing an adequate heat shrink ratio for coverage, one must consider the size of the underlying materials being covered—the larger the bundle, the larger the shrink ratio required. Prior to heat application, tubing must encase all wiring to result in the highest degree of wire insulation.
A: The stated ratio of heat shrink, such as 3:1, means that the tube has been expanded to three times its fully recoverable size. Once heat is applied, tubing will contract tightly around all interior components and "recover" the interlaying space.
For example, a 3:1 heat shrink ratio will recover to ¼ inch of a ¾ inch bundle, resulting in 67% shrinkage. Further, most heat shrink tubing will shrink in length, "longitudinally," around 5-15%; it is therefore important to measure enough tubing to cover the full length of the exposed area after heating.