The Kano model combines the anatomical design of the original BIRKENSTOCK insole with an additional latex heel cushion and an air-cushioned polyurethane sole. Adjustable metal pin buckle. Anatomically shaped PU insole. Oil and grease resistant PU (polyurethane) outsole. Birko-Flor® is a skin-friendly, tear-resistant and easy-care synthetic material, exclusively used by BIRKENSTOCK. Polyurethane (PU) is a flexible, water-repellent and dirt-repellent synthetic material that makes shoes easy to maintain. Polyurethane, also known as PU, is a synthetic material perfectly suited for outdoor use. It is water and dirt repellent and very easy to clean. Natural leather can be recognized by its untreated surface. BIRKENSTOCK deliberately does not treat surface grains and other characteristics. BIRKENSTOCK uses robust leather with a thickness of 2.8 to 3.2 millimeters as the upper material.