Our mules are an in-house design that is manufactured for us in Portugal using vegetable tanned calf leathers that will age beautifully over time. The uppers are crafted of a luxe Italian cowhide that has a supple hand with a waxy finish. For extra traction, the mules are built on a cork footbed atop a Vibram mini ripple sole. The upper will stretch and mold to your foot as it breaks in. SIZING: We recommend taking your usual Birkenstock Boston size, but if your feet have a higher instep you may want to consider going up one size. What's most important when putting these mules on for the first time is to assess where your heel is hitting on the cork sole and how much room you have in the front of the shoe. The upper will stretch, so if the mule feels a little snug at first against your forefoot but you have room in the front, you can trust that it will mold to your foot with wear. If you're unfamiliar with Birkenstock sizing, please click the "Measurements" link for size comparisons to standard US sizing. !split! !details! Italian calf leather Leather lining Suede footbed Cork sole Vibram mini ripple outsole !split! !measurements! US Sizing 5-5½ 6-6½ 7-7½ 8-8½ 9-9½ 10-10½ 11-11½ 12-12½ 13-13½ Mule Sizing 38 39 40 41 42 43 44 45 46