Shape fixing, or fixity, refers to the ability of an SMP to retain a temporary state, and thus store
strain energy, by cooling below a transformation temperature. Thermodynamically, shape fixing
results from a transition between a state in which changes in conformational entropy are dominant
(entropic rubber) and a state with limited chain mobility. Shape fixing can be quantified by use of
the measure, Rf (%) = εu/εm·100, where εu represents the strain after unloading, εm is the temporal