A transparent heat shielding multilayer structure is disclosed. The device further has an apparatus for applying an erecting force to the first mold plate such that in the open state of the device the first mold plate is inclined to the second mold plate, and an angle of inclination decreases with increasing degree of clamping of the device. The second end of the sealing cap is provided with a sealing bulge and a flexible sealing lip extending from said sealing edge, so that when the second end of the sealing cap is mounted over said sealing seat of said shank member, the sealing lip deforms and bends over towards the sealing edge, thus forming an enclosed channel therebetween. This drawn position is an initial setup position that allows fitting of the backrest for a particular user.