The ever-growing need for high-energy density and high operation temperature capacitive energy storage for nextgeneration applications has necessitated research and development on new dielectric materials for film capacitors. Consequently, various new approaches offering unique ways to tailor dielectric properties of polymers have recently emerged, and new materials such as dielectric polymer nanocomposites (PNC) are envisioned as potential next generation dielectrics. Establishment of optimized formulation and processing conventions is however necessary in order to achieve improvement in dielectric breakdown properties. Importantly however, such material development puts dielectric breakdown strength assessment of polymer films in a central role in guiding material development process towards highly optimized functional materials. This is not a trivial task though, as the current state-of-the-art breakdown strength measurement techniques rarely provide statistically sufficient amounts of breakdown data from the application point-of-view, thus leading to impaired evaluation of the practical breakdown performance in film capacitors. So many polymer films are used in capacitors since last many year. Their specific properties are high breakdown strength, low dielectric losses, and availability make this film well suitable for use as capacitor dielectric. At the moment, the typical energy density achieved with PP film at room temperature is about 1.2 J/cm3.Present work on this film focus on improving the permittivity, breakdown strength, thermal withstand ability, and thermal conductivity, by producing copolymers, bleding with other polymers, or adding inorganic particles. The influence of impregnating rapeseed oil on the dielectric breakdown behavior of thin metallized polypropylene (PP) foils used for high power capacitors was investigated. With oil impregnation the dielectric breakdown strength of the PP foil increases strongly. The breakdown behavior of rapeseed oil impregnated PP foils was compared to silicon oil and pentaerythrit-tetrapelargonate oil impregnated PP foils. Based on these experiments a guideline for the selection of impregnating oil for high power capacitors can be given. The breakdown strength of PP capacitor foils decreases with increasing temperature. In addition to this behavior, breakdown strength measurements performed as a function of temperature showed discontinuities for dry and saturated PP foils at defined temperatures. Investigations are performed to study the effects of variation of temperature.