The Boston boasts of the identical comfort of the Arizona in either the classic or soft footbed. Choose a soft suede to double as a slipper or a sturdier leather to take you for a dash between raindrops. No need to give up the comfort of your Birkenstock if you want to cover your toes. Oiled leather can be recognized by its untreated surface. Birkenstock purposely does not treat surface grains and other characteristic features. Birkenstock uses sturdy leather with a thickness of 2.8 to 3.2 millimeters as upper material.