The investigation of the thermal degradation or pyrolysis of vinyl polymers has been pursued from the theoretical and the experimental standpoint for polystyrene, polymethyl methacrylate, and polythene. The degradation of the first two polymers seems to be predominantly a depolymerization, while that of polythene is a process of random chain scission. The methods have been weight loss, viscosity studies, molecular weight distribution, osmotic measurements, and infrared analysis. The oxidative degradation of vinyl polymers has been extensively studied by Tobolsky, who emphasizes that a combination of analytical methods is necessary for a complete analysis of such a complex process. This paper presents the oxidative degradation of polyvinyl formal at high temperatures, studied by the infrared method in conjunction with weight loss, color development, and chemical analysis.