An insulating glazing unit including at least two glass sheets separated by, e.g., a gas-filled cavity. An insert serves for spacing the at least two glass sheets apart and has an internal face facing the gas-filled cavity and an opposed external face, together with a mechanism for sealing the inside of the glazing unit. The insert is in the form of a substantially flat profiled strip that girds the perimeter of the glazing unit by its internal face being pressed against the edges of the at least two glass sheets and held fast by a fastening device.