Abstract: The technical field of the invention is that of manufacturing boxes or cases or other packaging volumes which are foldable so as to be transportable in a minimum amount of space when empty: the present invention relates to such rectangular boxes comprising a base, four side faces of held thereon by a rim with two opposite ones of said faces being interconnected by foldable side elements enabling said two walls, when disconnected from the base, to be pressed one against the other, and a lid panel covering and holding said side faces remotely from the base; the two said interconnected faces are rigid insulating panels, the two lateral elements interconnecting them are belt portions, and the other two opposite faces are likewise insulating panels that are independent and that slide between the two first faces and against said belts when they are unfolded.