Measurements were made of tensile strength and heat-shrinkage force of rayon tire cords and of ir absorption spectra (unpolarized and polarized) of regenerated cellulose films in D2O vapor at elevated temperatures. The changes in crystallinity and frequency of OH absorption bands (intermolecular and intramolecular hydrogen bonding) in the crystalline region with increasing temperatures were determined. The ir absorption spectra of dry, regenerated cellulose films were also measured.