This waterproof performance sandal features the supportive BioCentric™ footbed and the Vibram™ Unaweep sole. The ZX/1® double, open toe strap design is fully adjustable and conforms to the foot's natural contours for a secure fit. Chaco medium width fits a narrow to medium width foot and wide width fits a medium to wide foot. In general, 1/2 sizes round down. M=medium, W=wide.