The internal wound element is constructed of two films of polypropylene dielectric having a metalization layer (Zn) with a thickness of some angstrom. The capacitance value is proportional to dielectric constant and area of overlap of the two plates and inversely proportional to the film thickness. The dissipation factor value is strongly related to the physical characteristics of the dielectric film. Polypropylene is definitely a proper choice for X2 capacitors since very often high frequency voltage is overimposed to the mains. Such a high frequency voltage affects the X2 cap overheating and material different from polypropylene would determine a very high power rate to be dissipated by the capacitor.