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
Chamois leather professional film and video camera viewfinders, as it provides comfort and absorbs sweat from camera operators who spend a long time with their eye planted on the viewfinder. Divers use towels made of chamois leather to dry themselves between jumps, as they can be quickly dried by squeezing them. Chamois leather Chamois leather () is a type of porous leather, traditionally the skin of the chamois ("Rupicapra rupicapra"), a type of European mountain goat but today it is made almost exclusively from the flesh split of a sheepskin. The leather is favored for its gentle, non-abrasive composition and absorption properties.