Why Brain Tanned?
Brain tanned hides are the only hides that can become wet and dry without losing their softness and flexibility. Most leather will stiffen and lose pliability.
When a hide is smoked, the non-water-soluble oil in the smoke bonds with the water-soluble oil in the hide, making all of it non-water-soluble. The smoke then provides lubrication to the fingers within the hide, which is what keeps the leather soft.