Stylist Notes The Birkenstock Madrid holds the distinction of being the oldest model in the Birkenstock collection, earning its status as a true classic. Introduced over 50 years ago as a "gymnastics sandal," this minimalist single-strap design has evolved into a beloved fashion staple. The upper is crafted from Birko-Flor®, a synthetic material renowned for its durability and skin-friendly properties. Birkenstock Womens Arizona Birko-Flor - Black