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
Victimless Leather it. Because the artificial leather is made semi-living, the project might be seen as speculative and provocative to some people – questioning whether it is better to kill semi-living beings rather than living beings. "One of the most common and somewhat surprising comments we heard was that people were disturbed by our ethics of using living cells to grow living fabric, while the use of leather obtained from animals seems to be accepted without any concern for the well-being of the animals from which the skin has been removed." artist Ionat Zurr uttered after showing the jacket to the public