Experimental measurements and Monte-Carlo (MC) modelling of the birefringence-strain, stress-strain and stress-optical behaviour of poly(ethylene terephthalate) (PET) are used, together with the analysis of orientation-strain and conformation-strain behaviour reported in Paper I, to give a detailed, quantitative interpretation and characterisation of its deformation-related properties. The difference between the stress-strain and stress-optical behaviour of PET that had been reported previously is confirmed. Except for the stress, the measured values of all the properties studied are in agreement with those calculated using the MC modelling, which suggests that not all of the junctions or the chains in the entangled PET network are elastically active. The results given by Kuhn and Grun theory are compared with those given by the MC modelling. The expected shortcomings of Kuhn and Grun theory are found. However, distinct from the behaviour reported previously for polyethene, the theory can be used to evaluate, semi-empirically, the stress-optical coefficient of PET. (c) 2007 Elsevier Ltd. All rights reserved.