Electrolytic capacitors are provided having an airtight housing, electrodes immersed in an electrolytic solution, electrical contacts connected to the electrodes, and a device for sorption of harmful substances. The device is made of a multilayer polymeric sheet (10), which is formed of an inner layer (12) of polymeric material, containing particles of one or more getter materials (11) for sorption of the harmful substances, and at least one protective layer (13) of a polymeric material impermeable to the electrolyte. All of the polymeric materials are permeable to the harmful substances.