The Birkenstock Kay SL mules combine the classic features of Tokio & Boston in one model. The strap over the instep can be lifted and brought back as a heel strap for even more stable support. The special sole is non-slip, allows for an ideal step progression, and is also oil and grease resistant. In the leather version, the EVA midsole comes with a particularly soft footbed, normal fit, color Black. Made of 100% leather.