calorimetric techniques have been used successfully for quantitative evaluation of flame retardant efficiency in textile materials. in addition, each of these techniques can also be used to study the mechanistic nature of the retardant action. for example, the heat of combustion of char measured by the oxygen bomb calorimeter provides some insight into the nature of the substrate degradation, while heat release data from the isoperibol calorimeter offers some qualitative information on the mode of retardant action the combination of the two calorimetric techniques provide a powerful tool for quantitative characterization of the nature retardant action. this is based on a simple model of cyclic burning which consists of two major chemical processes which are separate and distinct; a condensed-phase degradation (a fuel-generating process) and a vapor-phase combustion (a heat-generating process). the mode of retardant action can be elucidated and identified by measuring the total fuel generated from the substrate degradation and the heat released from the vapor-phase combustion. the application of the oxygen bomb and the isoperibol calorimetric techniques in the measurement of both fuel and heat generation is presented. specific examples of condensed-phase vapor-phase activity are discussed. 5 refs