Vionic Eureka Backstrap Sandal (Women) - BlackPowered by Vio Motion Technology to balance the whole you. The Eureka features a fisherman inspired leather upper with four adjustable straps and hook and loop closures for a secure, customizable fit. A soft microfiber footbed cushions every step, while Vionic's exclusive technology supports natural alignment and full body balance for all day comfort. Uppers: Leather. Microfiber covered footbed that offers a smooth feel and enhanced breathability.