Blank of cardboard or similar material, having cutout lines and score lines within a periphery cut out to a sheet and thus subdivided into elements of which certain are eventually to be glued flat against each other, said blank being adapted to be sold and stored flat, then ultimately to be folded, erected, and maintained folded thereby to constitute a container for objects to be shipped, the erection of the blank and the arrangement of the objects to be carried out manually and individually for each blank, characterized in that among the different elements of the blank there is at least one strip of a single thickness (7, 15-16) secured to at least one tongue (8-9) also of a single thickness located in prolongation of an end of said strip (7, 15-16) such that after setting up the blank and instruction of the container, the strip (7, 15-16) can be applied against the external surface of a wall (4b, 44, 2, 5-6) of said container, and that each tongue (8-9) can be folded down and applied against the external surface of a wall (5-6-7), adjacent said wall (4b, 44, 2), the setup container being maintained as to shape and closed irreversibly, and hence inviolably, by means of an adhesive (12) disposed between the strip (7, 15-16) and its tongue or tongues (8 and 9) on the one hand and the adjacent walls (4b-44-2, 5 and 6) on the other hand.