Birkenstock Women's Madrid Fashion Sandals, Mint Leather, 39 N Upper material: Birko-Flor - Made of acrylic and polyamide felt fibers, this material is a soft fabric with a smooth leather-like finish. Footbed: The original Birkenstock footbed - Featuring pronounced arch support, deep heel cup, and roomy toe box. Footbed molds and shapes to your foot. Sole material: EVA - Flexible, lightweight, durable and shock absorbing.