Used Size 12 Opanka Leather Women's Slingback Sandals. The Opanka Sandal also has a thin and flexible sole that allows you to feel the ground and move naturally. Whether you are strolling in the park or relaxing at home, the Opanka Sandal will give you the barefoot freedom you crave. Premium leather upper for a soft and durable feel. Leather lining for a smooth and breathable touch. Removable leather-covered insole that offers cushioning and support. Ultra-thin, flexible and foldable. Patented, ultra-thin, puncture resistant rubber sole.