By combining FTIR data of plasticized Estane (a polyester polyurethane copolymer) subjected to mechanical deformation with spectral differences as a function of added plasticizer, insight into the physical role of plasticization is gained. For Estane, the orientation functions and dichroic difference data show that, in static stretching, the soft domains reach orientation saturation before the hard domains. With added plasticizer, hydrogen bonding to the hard segments is disrupted and the glass transition of the soft domain decreases, indicating that plasticizer remains solubilized in the soft domain. On the time scale of the static experiment, plasticization diminishes the ability of both domains to reorient, while the plasticizer itself does not orient. With added plasticizer, neither domain reaches orientation saturation during the prestretching process, and dynamic distortion results in a similar response from both domains. Bimodal bands in the dynamic data indicate that the strain applied on a rapid time scale (20 Hz) allows resolution of the components of differently oriented bands.