The Sierra Adventure sandals offer the body comfort to endure long walks. The new Birkenstock polyurethane sole is light, flexible, abrasion-resistant and non-slip. The sole is attached to the cork foot bed and gives the sandal a robust, rugged look. This Birkenstock collection also features the classic anatomically shaped foot bed. The two fine black adjustable straps ensure that the foot is optimally supported by the foot bed. This way the feet, knees and back are relieved as much as possible. The Adventure Black is made from Birkoflor with a Nubuck look, a skin-friendly fabric that reduces the risk of blisters and irritation. This collection exists in several models for women and men. Sierra is the finer version of the Arizona Birkenstocks have a large fit. You may need a size smaller than your regular size.