This waterproof sandal features the Chaco Performance footbed and Z/2 wide strap style with the Vibram® Unaweep sole. This sole combines features from both the Colorado and Terreno soles, but is 20% lighter and provides greater slip-resistance and traction. Chaco medium width fits a narrow to medium width foot, and Chaco wide width fits a medium to wide width foot. In general, 1/2 sizes round down. M=medium, W=wide