I've long wondered how to design shoes with volumes and 3D features inside the top. When dealing with leather, there are two methods you may use: either you mold the leather to a preset shape or you make the details out of several stitched pieces. I didn't want to utilize any of them, so after several tries and failures, I came up with the concept of weaving pieces of leather to make three-dimensional forms.
The volumes in the design I built in this way would be made by combining all of the pieces and components. It could take the form of leather straps that are asymmetrical, round, or have some other straightforward geometric design.
I used this technical approach also when I cretaed shoes with combination of vegetabble tanned leather and you can read more about it in this post : "Innovative shoe designs ideas using a traditional shoemaking craft"