When selecting PTFE heat shrink tubing, you will need to know what size you require. Sizes are often given in the pre-shrunk state of the tubing. This will let you know how big of a wire or cable the tube can easily slide over. However, you will also need to know what size the tubing should be after it is shrunk. The amount the tubing will actually shrink is related to the ratio, such as 2 to 1, which means the tubing will shrink to about half of its original size, if it is fully shrunk.
Use the Shrink Ratio to Match PTFE Heat Shrink Tubing to Where It Will Be Applied
The location where you apply PTFE heat shrink tubing should be used to help pick out the right shrink ratio. When you need to fit the tubing over oddly-shaped components, like plug connectors, you will want to use a larger shrink ratio. Larger shrink ratios provide a slightly thicker wall, to protect the connector, than tubing with a lower shrink ratio.