Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
Ostrich leather amount of leather used. Designer handbags in ostrich leather are extremely popular as many luxury designers such as Prada, Hermès, Smythson, Bottega Veneta and Gucci, continue to make fashion statements with their wares made of exotic skins. Louis Vuitton has also popularized the use of ostrich skins, especially part of their runway collections. In 2006, the classic Louis Vuitton "Keepall 50 special" ordered in an ostrich skin was $10,800. Although such items are expensive, people seek them out because they are simply beautiful and different. It is quite easy to recognize an ostrich handbag. Different geographic regions have different demands