Controlled-atmosphere cone calorimeter is an interesting test method to study at the same time the effect of oxygen concentration and radiant heat flux on materials' fire behaviour and gas release. However, measurements in an extended range for these two variables can be tedious. To optimize the experimental measurement, this paper proposes a methodology based on the Doehlert design. The Doehlert method allows significant optimization of the number of tests. The optimization of measurement response is then accomplished using polynomial approximations to establish fire behaviour constitutive. Copyright © 2012 John Wiley & Sons, Ltd.