Shell Cordovan is a very specialized equine leather, made from the fibrous flat muscle (or shell) beneath the hide on the rump of the horse. It is known for its durability. The average size per 'shell' is 1.9 sq.ft. and thickness ranges from 1.5 to 2.3mm. The structure is very dense, it is not a leather that can be split. It is best suited for finishing in medium to dark colors.