The effects of changing the ratio of 4,4'-diphenyl methane diisocyanate (MDI) to ester on the stress-strain extension characteristics of various polyurethane elastomers are reported. The data was analyzed using phenomenological theories appropriate to low, medium, and high extensions and the effect of non-Gaussian terms are considered. Analysis of the high extension data using the Morris theory provides elastic constants which are characteristics of the polyurethane networks. The values of theses constants are discussed in the context of the expected variations of the morphology in these polymers. (C) 2015 Society of Plastics Engineers