AbstractInitial decomposition temperatures of various ureas have been determined using thermogravimetry and infrared analyses. Ranking of the compounds in order of thermal stability allows correlation between urea structure and resistance to thermal degradation.N‐alkyl substitution of an arylurea results in the most significant lowering of thermal stability (50–70°C) as compared to the standard (N,N′‐diphenylurea) whereas orthosubstituent effects and electronic effects are present but lesser in magnitude. The large steric effect is postulated to indicate the necessity of rotaion of the nitrogen–carbonyl bond during dissociation in order to establish the proper geometry for isocyanate bond