In insulation materials several chemical and physical deterioration processes arise, such as thermal and electrical ageing, and moistening, due to operational and environmental stresses. As well as electrical strength, these deterioration processes influence the dielectric processes, the conduction and the polarisation of the insulation. My thesis reviews aging phenomenology and life modeling, illustrates different approaches, showing their advantages and raises problems relevant to practical applications of models and evaluation of materials endurance. It is shown that the factor predominant on aging acceleration due to the voltage distortion is voltage-peak increase, but also waveform slope and voltage rms value have statistical significance. Life models are obtained for XLPE and PP insulating materials, which show the endurance of the two materials to aging under non-sinusoidal conditions. Phenomenological and physical models are examined, considering also a statistical approach, with applications to experimental results. Finally, statistical processing of data and determination of model parameters are mentioned and graphical methods for material characterization are proposed.