Women's Vionic Opal Mules This slip-on mule offers an easy, modern look with support-focused comfort. The leather upper adds a polished feel, while the open-back design keeps it simple for everyday wear. VIO MOTION™ Technology provides contoured arch support, shock-absorbing cushioning, and a deep heel cup for stability. Finished with a 1.125" heel and 0.75" platform for a balanced lift.