In this paper, a moire interferometry technique was used to study the viscoelastic strain distributions within and across the interfaces of multilayer thermoplastic elastomers, which were fabricated as models for functionally modulus-graded materials. Two types of interfaces, those formed from miscible and immiscible pairs of the same thickness, were fabricated within multilayer thermoplastic samples. The analysis of the moire fringe patterns indicated that there was a large normal strain, epsilon(y), concentration at the polymer interfaces formed from the immiscible or partially miscible pairs. However, this large normal strain was not observed at the interfaces formed from the miscible pairs. These results suggest that the magnitude of strain concentrations at polymer interfaces within functionally modulus-graded materials could be significantly reduced by extensive chain interdiffusion, which could be promoted by careful selection of miscible polymer pairs. (c) 2005 Wiley Periodicals, Inc.