MATERIAL The signature slip-on clog from BIRKENSTOCK - the Boston. A casual-wear staple, perfect year round. Featuring a simple, adjustable design and contoured cork footbed that forms to the shape of the foot, the Boston is a timeless and perennial favorite. This classic model comes in an especially cozy version with genuine shearling lining the footbed and the upper. The perfect shoe for cozy winter evenings! The upper is made from soft suede.