Women's Birkenstock Vegan Boston Nubuck - Black - Slippers The birkenstock boston clog is a veritable classic that can easily be worn all year round. This popular sandal has been given an update in a new material. With a vegan version now available. It is entirely free of animal products. As verified by independent testing laboratories. The upper is made from the skin-friendly. Hard-wearing synthetic material birko-flor in a sophisticated nubuck look.