The principle of the method specified is measuring the heat flux supplied to a test sample as a function of time or temperature, while the test sample is subjected to a temperature schedule under a specified atmosphere. A reaction is marked by the release of energy from the sample, resulting in an exothermic peak in the heating curve. Integration of the recorded peak area as a function of time gives a measure of the energy of the reaction. Applies to phenolic resins with exothermic behaviour, such as resols or mixtures of novolaks with hexamethylenetetramine or other curing agents.