Material: • Upper material: Birko-Flor®: Birko-Flor® is a skin-friendly, tear-resistant and easy-to-care-for synthetic material which is exclusively used by Birenstock. • Insole: Polyurethane: Polyurtehane (PU) is a flexible, water- and dirt-repellent synthetic material which makes footwear easy to care for. • Footbed material: Polyurethane: Polyurtehane (PU) is a flexible, water- and dirt-repellent synthetic material which makes footwear easy to care for.