Upper material: Oiled leather is one of our favourite types of leather. Its oily waxed surface makes for a unique colour effect and develops a beautiful patina. The oily finish of our natural leather products results in colour variation, making each and every pair unique.Insole: Natural leather can be recognized by its untreated surface. BIRKENSTOCK purposely does not treat surface grains and other characteristic features. BIRKENSTOCK uses sturdy leather with a thickness of 2.8 to 3.2 millimeters as upper material.Footbed material: Cork is a sustainable material extracted from the bark layer of the cork oak. This natural product is insulating and offers very good cushioning.Outsole: EVA (ethylene vinyl acetate) is a high-quality, very light, elastic material with extremely good cushioning. As a result, it smooths out slight irregularities in the floor and ensures that every step is softly cushioned.