Most products during their melt processing will have been cooled at a high
rate and the degree of crystallisation will be significantly less than at thermodynamic
equilibrium. With time the degree of crystallisation will increase, and because of the much
higher density of the crystalline phase, the volume contraction with time can be as high as
0.5% (compared with only about 0.1% for amorphous materials). Volume contractions of
this magnitude will, if constrained, generate significant tensile stresses, and in combination
with a decline in ductility they have been known to be the primary cause of product failure