After the samples are hydrated for 1 week (ii), the absorbance increases in 3-9 THz due to the water molecules adsorbed in the samples. In addition, a band structure appears at 6.5 THz in the spectra of (b). This band is known as a characteristic band for -nylon-6, and this band does not disappear after the samples are vacuum dried again. This result shows that the  crystalline change is induced by the hydration in the 76 %RH chamber. In this study, cycles of drying and hydration process are performed for each sample in the vacuum dried chamber (40 C) and the hydration chamber (100 %RH), to make their macromolecular structure in equilibrium for the water adsorption.