The special feature of the "Knapsack" is in the detail. The steel band processed in the edge of the bag hugs the body, so that the bag closes even without a zipper. This bag edge can also be folded over. This not only makes the bag more theft-proof, it can also be made smaller by folding the edge back several times.
Christoph Ulrich Seyferth developed a smooth-running ball bearing consisting of a metal hook and a holder made of POM plastic so that the folding of the bag's edge literally works in the blink of an eye. Solidtec injection molded the parts for this bracket within a few days. The advantage of rapid tooling over 3D printing is literally obvious here and in the durable handling, because: The holder pieces must be UV-resistant, robust, stable, color-fast and as smooth as possible so that the bag serves its purpose for many years.
Special attention was paid to the interaction of the components to guarantee that the edge of the bag can really be folded down smoothly. It was important that the metal hook could slide when the bag was closed. The interaction of the hook with the holder we made makes this possible in the smallest of spaces - the special and casual handling of the Knapsack will work perfectly for years.