New BIRKENSTOCK Madrid Birko-Flor Black Sandals size 38/7 The original BIRKENSTOCK Sandal. A strap, a buckle, and a contoured cork footbed are masterfully combined to create the Madrid. The upper is made from the skin-friendly, hard-wearing synthetic material Birko-Flor®. Anatomically shaped cork-latex footbed Upper: Birko-Flor® Footbed lining: suede