A model system, a tri-layer of polycarbonate/poly(ethylene terephthalate)/polycarbonate, was used in this study to investigate the interfacial properties of an immiscible polymer blend system. The model system was compression molded and quenched in three different media : ice, water, and hot water. The interfacial properties of interest were the through-thickness residual stress profiles and the interfacial strength. A method of estimating the interfacial strength of an immiscible polymer blend was also proposed, enabling the prediction of failure. The method was based on a single-notch 4-point bending test. The load at which failure occurred was then analyzed using finite element stress analysis to resolve the interfacial stress, i.e., the strength of the interface.