Leather or Suede Upper. Adjustable Slingback with Buckle. YOUR NEW FAVORITE FLATS: Elevating the classic sling back in a variety of luxe leather and suede colors to polish any 9-to-5 suit or casual denim. EVERYDAY SUPPORT: A podiatrist-designed footbed built into every pair of Vionic sandals, slippers, active shoes and flats promotes stability from the ground up.