The capacitor (2) according to the invention comprises: an enclosure (4); an insulating material (6) contained in the enclosure (4); a capacitive device (8) comprising two conductive layers and at least one dielectric layer formed from a dielectric material and inserted between the two conductive layers; and a protection device (12) comprising a mechanism (40) for disconnecting the capacitive device (8) in case of overpressure in the enclosure (4); and characterized in that it further comprises, inside the enclosure (4), a degassing material (58) capable of releasing gas at a degassing temperature (Tgaz) below the decomposition temperature of the dielectric material to generate an overpressure in the enclosure (4).