WIMA's FKS 3 polyester dielectric (PET) employ ultra-thin film to achieve high capacitance values in small box sizes for use in applications like coupling and decoupling.

In the case of film and foil types, the electrode is not applied like it is for the metallized capacitors but is wound with the dielectric as a metal foil. Due to their lower series resistance, the components produced this way have excellent pulse and current carrying capability, as well as a very high insulation resistance.

The film/foil construction is mainly used for capacitors with smaller capacitance value. The advantage of this construction principle is the easy contactability of the metal foil electrodes and the good pulse strength. To avoid breakdowns caused by weak spots in the dielectric, the insulating film chosen is always thicker than theoretically required by the values which are determined from the specific breakdown strength of the material.