Abstract: The invention relates to a vacuum bulb (1) including a sealed chamber (4), two electrical contacts (7, 7?) and a dielectric coating (12) which covers the outer surface of the chamber (4). This coating (12) includes at least two layers, an overmoulding layer (14) made of a synthetic material and an intermediate layer (13) made of silicone interposed between the outer surface of the chamber (4) and the overmoulding layer (14). According to the invention, the intermediate layer (13) is discontinuous and localised on the metal portions of the chamber (4) so as to cover at least partially the outer surface of the metal portions, where the silicone of the intermediate layer (13) includes hollow bodies, where these hollow bodies are compressible, and have a skin made of a thermoplastic material. The invention also relates to a switchgear including at least one such vacuum bulb (1), in particular a circuit-breaker pole.