The back panel is part of the free standing outdoor shelf and is made of Aluzinc steel. A complete section of the free standing shelf consists of one back panel, two uprights and two galvanized floor panels with height 85 cm and depth 30 cm. To build additional sections, you need one upright along with one panel for each section. We recommend at least one back panel, preferably placed in the middle, for a free standing shelf consisting of three sections.