Why don't we use leather outsoles?
First, leather is a very fickle material.
- It's quite stiff at first and has a long break-in period.
- It's slippery to the point of hazard
- It wears away when wet
- It can get waterlogged and stiffen beyond repair
Second, we haven't been able to create a "hollow heel" with leather. So, if we went with leather outsole, you'd end up with something like the Vivobarefoot Lisbon.
I do concede that leather outsoles look better! Fortunately, we're developing a new outsole that will better mimic the look of leather, while keeping the flexibility, non-slip, water-resistant, and hollow heel benefits of synthetic.