Monomolecular water in a solid polymer, which has no effective hydrogen bonding sites, was revealed by temperature-variable Fourier transform infrared spectroscopy to be condensable and crystallizable. Ice I-h formed in the polymer matrix was grown by vapor deposition and was reduced by sublimation. Moreover, rapid cooling induced crystal growth by vapor deposition during heating (revapor-deposition). These results indicate the requirement of a change in the generally accepted understanding of the thermal responses of water in a polymer matrix and give rise to a problem for general interpretation of the category of water in a polymer matrix based on calorimetrical analysis at very low water contents.