The thermal oxidation of unplasticized cellophane film at temperatures from 90 to 140°C was evaluated by the increase in absorbance at 265 nm and the decrease in percent transmission at 1725 cm^-1. Treatment of the aged films with aqueous NaBH₄ solution almost completely eliminates the peaks, indicating that the absorption in both regions is due almost exclusively to carbonyl moieties. A water wash partially decreases the absorbance, showing the presence of low-molecular-weight species. The oxidation of the film follows first-order kinetics with rates close to those found for decreases in tear strength and depolymerization of cotton and rayon fabrics. The reaction mechanisms appear not to be affected by temperature. The infrared spectra of the film and of the water extract of the aged film are essentially the same as those found for naturally aged linen.