Such qualities of vegetable tanned leather create endless possibilities for an artist or craftsman. For most of my projects I use top grain vegetable tanned leather which I get from Tandy Leather Company . Much like paper, commercially available leather comes in various thicknesses or weights. The weight you want to use depends on the type of your project. Thinner leather lends itself to sharper creases and significant stretching.
Thicker pieces are sturdier and keep the shape better.
For my masks I mostly use thin 3-4 oz. leather. My favorite most versatile tool in the whole arsenal is my right thumb. Nothing quite like it. Of course it you're a lefty you may want to consider your left thumb. Come to think of it, both thumbs compliment each other quite nicely.