Tension set is defined as the proportion of applied strain remaining after a rubber piece has been stretched and allowed to recover in specified manner. It is an important property for rubber components that are subjected to tensile stresses either continuously or intermittently.

Tension set is determined by stretching a test specimen of standard dimension by a specified percentage in a suitable apparatus for a specified time and temperature and then allowing it to recover. It is indicated as permanent set retained by the test specimen expressed as a percentage of initial strain given to it.