Birkenstock Slides, size US 10-10.5/EU 41, LIKE NEW, Pewter/Silver Metallic Color with beige insole and silver bottom. Birko-Flor® is a durable, synthetic material which is used exclusively by BIRKENSTOCK. The surface made of hygienic PVC plastic repels dirt and water, and is easy to clean. Soft fleece on the inside of the straps ensures maximum comfort against the skin. Birko-Flor® opens up a wide range of creative possibilities when it comes to design. It can be lacquered, coated, glued and designed with a metallic finish.