Studies have been carried out to evaluate the fire-retardant properties of zinc hydroxystannate, relative to those of antimony trioxide, in resins based on the bromine source, DBNPG, containing various inorganic fillers. The effectiveness of ZnSn(OH)~ and Sb203 as flame retardants depends on several factors including incorporation level of the additives and fillers, and bromine content of the resin. CaCO 3 is a poor filler in these resins, talc and AI203 are reasonably effective and ATH is good, particularly at high loadings (>50phr). In general, Sb203 gives optimum performance in ATH-filled resins, whereas ZnSn(OH)6 exhibits a marked flame-retardant synergism with anhydrous AI203. Although Sb203 increases smoke emission from unfilled and alumina-filled resins, ZnSn(OH)6 significantly reduces both the rate of production, and the maximum level, of smoke generated from these materials. In addition, the ZnSn(OH)6-AI:O 3 combination markedly inhibits the evolution of carbon monoxide from burning resins and is clearly an excellent overall fire-retardant system for this type of polymer. Thermoanalytical studies provide evidence for a combined condensed/vapour phase mode of action, in which the ZnSn(OH)6-AI203 system catalytically promotes the dehydrobromination of the resin and leads to the subsequent formation of volatile metal halides or oxyhalides. These processes lead to an increase in the yield of thermally-stable char, at the expense of flammable products, and result in the introduction of combustion-inhibiting species into the flame.