Abstract: There is provided an insulating unit, such as a double-glazed sealed window unit, comprising at least two spaced-apart transparent plates. The plates are sealingly joined together around their peripheral edges by sealing means, thereby to form a sealed chamber in which there is enclosed a medium such as gas, air or liquid. Means are provided to permit a pivoting movement of at least one of the transparent plates towards and away from an opposing plate, thereby to increase or decrease the volume of the enclosed medium in response to changes in the temperature of the transparent plates.