AbstractAn investigation of the burning behaviour of a series of halogenated polyester resin formulations has been carried out using the Cone Calorimeter technique. The data obtained clearly indicate that zinc hydroxystannate (ZHS) is more effective than antimony trioxide (Sb2O3) in reducing the average and peak rates of heat release in a chlorinated resin and in decreasing the peak rate of heat release in a brominated resin. The decreases in average heat release rate in the brominated resin are similar for ZHS and Sb2O3. Hence, at an addition level of 2 phr (parts per hundred of resin), ZHS reduces the average heat release rates of a chlorinated and a brominated resin by 41% and 26%, respectively, and the peak heat release rates of the same resins by 38% and 39%, respectively. The degree of smoke suppression exhibited by ZHS in these Cone experiments is significantly greater than that given by Sb2O3. In general, the correlation between Cone Calorimeter data and results obtained using other laboratory fire tests (UL‐94, LOI) is poor, except in the case of smoke density measurements, where the correlation with NBS Smoke Box data is remarkably good. No correlation is observed between the measured values of CO and CO2output by different test methods, although it is now generally considered that small‐scale fire tests cannot be used to predict gaseous concentrations in real‐fire situa