Insulating structure

Claim 1

Insulating structure for use with a window which is enclosed within a rectangular window frame which defines a rectangular window opening, said insulating structure comprising: (a) a rigid rectangular envelope having an opening along one side, the envelope being adapted to being fastened in a wall with the opening facing the window opening, and located in a plane that is offset from the plane of the window, the envelope being substantially air-tight except for the said opening, the envelope consisting of two similar rigid rectangular sheets held in spaced parallel relationship by spacer blocks extending around three side edges, the fourth side edge being free of a spacer block and constituting the said opening, the side of each sheet which faces the interior of the pocket having a flat smooth continuous surface, (b) a main sheet of insulating material slidable in the envelope from an inoperative position in which it is entirely enclosed in the envelope to an operative position in which it is substantially outside the envelope and is co-extensive with the window opening and in front of the window, and (c) a groove which extends entirely around the inside of the window frame except for said opening for receiving the edges of the main sheet when the main sheet lies within said window opening to form a tight seal around the edges of the main sheet.