- BIRKENSTOCK/Birkenstock flip-flops This classic flip-flop features an elegant large metal buckle. Comfortable and easy to wear. The lining of the semi-fine insole is covered in soft smooth leather that matches the color of the shoe. Upper Made of high-quality, soft natural leather. Upper: pebbled cowhide. Sole: cork midsole and EVA rubber backing. Size: 35-45,