The thermal properties of the energetic material 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-tetracyclo-[5.5.0.0(5.9).0 (3,11)]-dodecane (HNIW), also known as CL-20, have been investigated by DSC, TG, ARC, HFC and simultaneous TG-DTA-FFIR-MS. The solid-solid phase transitions and the reversibility of these phase transitions were explored using DSC. A heating rate study was performed and the DSC traces show the possibility of a multi-step thermal decomposition of CL-20. The enthalpies of reaction and onset temperatures were determined for various heating rates. The kinetic parameters were found by means of the ASTM E698 method and were verified by ageing experiments. A model-free kinetic (MFK) analysis was performed on the DSC heating rate results. TG experiments were conducted to investigate the effects of various heating rates on the mass loss of CL-20 and its onset temperature. The TG results were analyzed using MFK and ASTM E1641 methods. ARC measurements were performed to investigate the thermal stability of CL-20. The thermal behaviour of CL-20 at various pressures of argon was studied by heat flux calorimetry (HFC). The gaseous products from the decomposition of CL-20 were determined by simultaneous TG-DTA-FTIR-MS experiments in air and in helium. The thermal stability at different isothermal temperatures (190, 195, 200 and 205 degrees C) was studied, using the same technique. (c) 2005 Elsevier B.V. All rights reserved.