After assembly the condenser is vacuum
dried and impregnated with a dielectric fluid. Instead of a high-quality paper
(‘condenser paper’, 10 to 30 µm thick) plain plastic films (e.g., polystyrene) or
mixtures with plastic films and paper are now in use. Rolled condensers will
have high inductance, if the metal electrodes are only joined at their ends or
at some intermediate positions. Very low inductivity can only be gained if the
technique of ‘extended foil construction’ is applied. In this method each of
the two metal foil electrodes are on one side extended beyond the dielectric
foils and after rolling and pressing continuously joined (welded) on each side
to form the end caps.