Fiber-optic evanescent wave infrared spectroscopy was used for the study of water diffusion in Teflon and has provided valuable information about the structure of water in amorphous hydrophobic polymers. Time-dependent absorption measurements were carried out in two spectral ranges: 3000-3800 cm(-1), associated with the O-H stretching mode, and 1620-1670 cm(-1), associated with the H-O-H bending mode of water. The results indicate that the IR spectra could be expressed as a superposition of spectra due to two species of water molecules: strongly and weakly hydrogen-bonded. We suggest that water molecules form clusters with strongly hydrogen-bonded molecules at the cores and with weakly hydrogen-bonded molecules at the external parts of the clusters. A mathematical model, based on a linear diffusion equation with a moving boundary, gave a ratio of 3.5 between the total number of molecules in a cluster and the number of water molecules at the core of the cluster.