Empirical molar group contributions to the thermal combustion properties measured by microscale combustion calorimetry were determined by multiple linear regression of data for engineering polymers of known chemical composition. Char yield, heat of combustion and heat release capacity of polymers calculated from their chemical structure using optimized additive molar group contributions were in reasonable agreement with measured values for these properties. The relationship between the thermal combustion properties and the results of standardized flame and fire tests (i.e., flammability) was examined statistically for an expanded data set. Published by Elsevier Ltd.