Sealing plug with a pressure-compensating chamber

A plug to hermetically seal an aperture in a sheetmetal, or in the floor of a vehicle, comprising:

• a cap covering the aperture and comprising an external, circumferential flange resting on one side of the sheetmetal or of the floor and fitted with a first circumferential seal, an affixation portion entering said aperture and a second circumferential seal configured at the cap or at the affixation portion and being a distance from the first seal and resting against the sheetmetal or the said floor, a cavity being subtended by the sheetmetal or said floor, the two seals and at least one wall of the plug, wherein said plug includes a pressure-compensating chamber, which communicates with the cavity and which compensates a change in pressure, caused by a change in temperature, inside the cavity, by changing the volume of the pressure-compensating chamber;
• the communication between the cavity and the pressure-compensating chamber which compensates the change in pressure is constituted by at least one duct.