Birkenstocks! BAD IDEA. There isnt anyone out there to phone for help, so you really do need to understand from written instructions. But after a few days wear, the straps loosen and its a good fit. the screws are supposed to go into threaded portion and they were off by atleast 2 inches. Extremely light weight, so you dont notice it at all while running. Its worth the price. These have been clearly worn before and absolutely no effort was made to conceal the fact. Lo lleve a garantía y me dijeron que no entraba porque estaba mojado, el único líquido que pudo tener fue el sudor por lo que NO los recomiendo para correr porque por el sudor es suficiente para que pierdan la garantía aún y cuando se supone que es contra salpicaduras y sudor. Worn these for years .