The skin-core structure of injection-molded plates of poly(ethylene terephthalate) (PET) has been investigated using Confocal Micro-Raman Spectroscopy (CMRS) and Differential Scanning Calorimetry (DSC). CMRS has proved to be a useful tool for finding out about quantitative conformational changes in polymeric materials. In order to obtain a complete picture of isomer distributions in the injection molded industrial PET samples, spectroscopic measurements were correlated with DSC measurements. The spectroscopic results reveal two different structural zones related to the fabrication process: a skin layer and the core. The correlation between the apparent degree of crystallinity obtained by DSC and the percentage of the trans isomer obtained by CMRS has allowed the latter parameter to be separated into crystalline and amorphous trans isomer and to follow its change along the injection molded plate.