The effect of mechanical deformation, produced either by an externally applied strain or by an indentation imprint, on the local spectral response of a polymer was studied by micro-FTi.r. spectroscopy. Two types of specimens were used, a urethane-acrylate polymer film, and a SiC/urethane-acrylate model composite, respectively. The width R of the interfacial zone beyond which the fiber has no influence on the matrix, a parameter that plays a key role in micromechanical models of stress transfer in composites, was measured by micro-FTi.r. for the first time.