The reactivity towards CO2 of seven types of commercial coke used in stone wool production has been measured in a thermo gravimetric analyser (TGA). The cokes originated from Western and Eastern Europe and from China. For three of the cokes, the porosity, density and surface area were determined. The directly measured porosities of the cokes was slightly low, indicating that there are pores that are not connected with the outer surface. This is supported by the measured densities and microphotos. The measurements showed that the Chinese cokes were the least reactive while the European cokes made on American coal were the most reactive. The reactivity of the one Eastern European coke in the measurements had an intermediate reactivity. Simulations with a cupola model show that 25% more coke is needed for stone wool production if the coke is changed to a type with half the reactivity towards O-2 and CO2. The TGA method proved to be a good method for ranking the coke with respect to reactivity with CO2. (C) 2004 Elsevier B.V All rights reserved.