Natural leather starts as an animal hide, with its own character and imperfections. It’s largely made of proteins and water. Left untreated, it would turn brittle and decay because of the water content. To prevent this from happening, leather is tanned by replacing the water molecules found in the animal skin with either a natural or synthetic chemical that binds to the proteins in the hide and stabilizes them. The resulting leather doesn’t decay, and is supple, durable, and strong.