Boston Suede Embossed in Color Corduroy Sienna Red 。Upper material: Material combination For this shoe, a combination of materials was used. You can find more information on our main materials in our Material Guide. Insole: Natural leather 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 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 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.