This work investigates the electrothermal lifetime of a commonly used polyimide wire insulation material, Kapton((R)), through the use of thermogravimetry (TG) and breakdown voltage testing. From TG, an isoconversional model-free kinetic evaluation was used to obtain a relationship between the activation energies of degradation for Kapton as a function of weight loss. By relating the electrical life theory and the TG theory through the model defined by Toop (IEEE Trans. Dielectr. Electr. Insul. 1971, 6, 2), the electrothermal lifetime of Kapton has been calculated for conditions of 12 and 14.7 kV over a temperature range of 250-400 degrees C. The resulting model can be used to make lifetime predictions for wire insulation degradation in aging aircraft for improved safety and risk assessment. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1639-1644, 2013