Birkenstock Unisex Arizona Slide Fashion Sandals, Black Leather, 44 N Birko-Flor / Birkibuc Synthetic sole Upper material: Birko-Flor - Made of acrylic and polyamide felt fibers, this material is a soft fabric with a smooth leather-like finish. 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.