We derive the minimum thickness from the length, because soil pressure on the side walls increases with it: 2 mm up to a length of 70 cm, 3 mm up to 140 cm, 4 mm up to 190 cm and 5 mm above that. This minimum thickness is included in the price; a thicker sheet can be selected in the configurator for a surcharge. In addition, the closed body, welded all around, distributes the soil pressure across one continuous system, making it considerably more dimensionally stable than a bolted kit. A horizontal stiffening profile supports the side walls from the inside, and the double-folded top edge reinforces the upper rim.