RS Pro Flexible Polyolefin Heat Shrink Tubing with 2:1 Shrink Ratio. From RS Pro a range of high quality, easy to use heat shrink tubing made from flexible, flame retardant Polyolefin. The shrink ratio of this heat shrink tubing is 2:1 which means it shrinks to half of its original diameter. This heat shrinkable tubing meets the requirements of a wide range of high tech and industrial standards including SAE-AMS-DTL-23053/5 class 1