Birkenstock Unisex Arizona - Oiled Leather Biscay Bay Oiled Leather Sandals 37 (US Women's 6-6.5) Regular Leather / Nubuck / Suede Upper material: Oiled Leather - Thick yet supple leathers without additional dyes to keep the leather breathable, durable and comfortable. The original Birkenstock footbed - Featuring pronounced arch support, deep heel cup, and roomy toe box. Footbed molds and shapes to your foot. EVA Sole - Flexible, lightweight, durable and shock absorbing.