JJill Kork-Ease Challis ll Mules. Black. Size 9. NEW w/o Box. The #1 reason to love these mules is because they’re backless and thus slip-on. But, besides that… they’re leather but lightweight; they’re casual but chic; and, they’re designed with an extra comfortable stacked heel, a suede covered footbed, and a high traction rubber outsole. 3.5” heel.