AbstractA fire test device suitable for small‐scale, comparative testing as a first step in investigating the performance of fire retardant materials is described. The procedure developed is not intended to predict the performance of a given material in a real fire, since the local conditions can be extremely variable. However, the parameters in the device can be varied over a wide range to screen the performance of various materials in given situation. Typical results for an intumescent mastic consisting of epoxy resin, hardener and melamine phosphate are quoted, together with appropriate calibration curves. A method of estimating the thermal resistance of the developing char is also discusse