In any polymer blend system, the nature and thickness of the polymer interface can have a significant influence on the overall performance of the blend. Consequently, it is important to understand the nature of the interactions between the various blend components to effectively design blend combinations with desired end-use properties. However, because of the inherent level of difficulty, the quantitative measurement of the interface thickness in immiscible polymer blends has not been accomplished or reported in the literature. Atomic force microscopy in the tapping mode has been employed to establish a systematic methodology to measure the relative interface thickness of seven types of coextruded multilayer polyolefin films. Criteria have been developed to define profiles of the interface and estimate the interface thickness from these profiles. The effects of tip indentation on the measured value of the interface thickness are also considered. The atomic force microscopy method presented here allows for a direct quantitative estimate of the interface thickness in multilayer polyolefin films, which in turn provides a significantly better understanding of physical properties such as tear in coextruded blown films and the toughness/stiffness balance in injection-molded impact copolymers. (C) 2007 Wiley Periodicals, Inc.