I have checked with a local leather shop here. He had the thick leather. I talked with the guys there at the shop, and the most limiting factor apperars to be making a "buck" or mold to form it with. In the begining of the Brooks web site there is a machine running. From what I can see this is the mold or buck causing the leather to be pressed into the seat shape. I have read some where (so totaly unsubstantiated) that some type of dressing/salve is added to the leather to help it maintain its shape.