Birkenstock Arizona Jelly Two Bar Mule The Birkenstock Arizona Jelly Mule is a modern take on the classic mule with two bar straps across the front and finished with the statement Birkenstock branded buckle. Crafted from comfy light weight jelly rubber, the foot-bed has been contoured to conform to the shape of your foot - with arch support and an extra layer of cushioning for optimum comfort. Upper: Rubber Sole: Rubber Fit: Standard