Linear Thermal Shrinkage or Free Shrink is defined as the irreversible and rapid reduction in linear dimension, in a specified direction, occurring in film exposed to elevated temperatures.
Shrinkage in this way is related to the material of the film and internal stresses locked into the film (by the manufacturing process). The Film Free Shrink Tester consists of a small, circular aluminium block, electrically heated and controlled by a temperature controller. Using aluminium foil discs with silicon oil, the test piece is placed into it to accelerate shrinkage at selectable temperatures.
• ASTM D2732