2 things that make this bag no ordinary - its Fabric & its Lock. Fabric is the same as used for soft-top convertibles: acrylic on the outside, polyester inside, and the interlay made of rubber and thus water-proof, cleanable, temperature-resistant, non-discolouring & stiff(no surface strain). The same material that used by Ferrari, Jaguar, Mercedes or Porsche. The lock was originally developed to secure the softtops of convertibles. When engaged, it guarantees absolute reliability & cannot open on its own. Pefect for A3 drawing and max book air carrying around on board