Because only vegetable tanning agents, and no heavy metals, chrome or other harmful substances are used to treat the leather. And no additional chemical sealers are used. This is good for the environment and makes the leather particularly non-allergenic. Vegetable tanning also retains the natural breathability of the leather. This results in exceptional wearing comfort. By the way, each strap is truly unique: because it's a natural product, each strap looks a little different from the other. The leather also acquires an individual patina over time, giving the watch even more character.