leather suitable for outsoles, often 8 irons or thicker veg-tan cow leather
Outsole leather is often rolled by the tannery. Some makers keep rolling machines to roll uncompressed bend leather themselves, or use other methods like hammering over a lapstone or wetting and compressing between boards in a vise.
Outsole leather is often cut from the butt of the hide. (Handmade Shoes for Men page 133)