The film shrink tester is used to measure the effect of temperature on plastic films. The application of heat causes certain plastic films to rapidly contract; this effect can be used to seal and pack many items from food to consumer goods. The shrink effect is due to internal forces locked into the film during manufacture being released by heating. It is also known as linear thermal shrink or free shrink. The amount of shrinkage is dependent on the film type, thickness, and sealing temperature. Testing the percentage shrink of a film ensures that it is suitable for a particular packaging application and establishes the correct temperature for that application.