The aim of this research was to explore the use of a stepwise regression analysis to determine the post-consumer recycled polyethylene terephthalate (PET) content in PET sheets. Six kinds of PET sheets with varying percent of virgin (V) and recycled (R) PET contents were produced at Peninsula Packaging Company (Exeter, CA, USA). The optical, thermal, barrier and thermo-mechanical properties of the PET sheets were evaluated as function of RPET contents. There was a statistically significantly difference between the UV and visible light absorption in the region between 200 and 350 nm and 670 and 700 nm, respectively. Color measurement indicates that more RPET contents in PET sheets lead to greyer, greener and more yellow color. DSC indicates that the melting (T_m) and cold crystallization temperatures follow a semi-linear trend with the amount of RPET in the blends. Intrinsic viscosities were statistically significantly different between 100%V and 100%R PET sheets. The results of ¹H NMR indicates that protons of end groups in 60V40R, 40V60R and 20V80R PET were higher than 100V PET (α=0.05). A tentative stepwise regression model emerged with an adjusted R² of 0.9740 for predicting the amount of RPET, with intrinsic viscosity, UV, color, T _m, and oxygen permeability values as predictor variables. This model was developed for a specific mechanical RPET stream provided by the ECO2 company (Modesto, CA, USA). At this stage, it is not applicable for other recycled PET streams and products without new studies.