Birkenstock Boston Shearling Grey size 38 Upper material: Suede Suede is a split leather with a napped finish. It has a velvety surface and is very soft to the touch. Insole: Shearling Shearling is high-quality, soft sheep-or lambskin. Footbed material: Cork Cork is a sustainable material extracted from the bark layer of the cork oak. Condition: Used, with some marks of use.