Response function of ammonium perchlorate (AP) has been studied. An unsteady model of AP combustion has been used based on the recent experimental findings reported. The key findings of this work are the good comparisons with experimental results, which until date had not been predicted accurately. Variation of thermal properties as a function of temperature in the condensed phase predicted the experimental data better. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.