Leather thickness is measured in millimetres and should match the project. Wallets use 0.8–1.5mm, card holders 1–1.5mm, bags 2–3mm, and belts 3–4.5mm. Too thin and the piece loses structure; too thick and it becomes hard to stitch, fold, and finish cleanly.
Vegetable-tanned leather is leather that has been tanned using plant-derived tannins in a slow, traditional process. It is firmer and more structured than chrome-tanned leather, takes edge finishing and burnishing well, and develops a patina with age and use. It is the standard choice for hand leatherwork — wallets, belts, bags, and small goods — because it cuts cleanly, stitches well, and responds predictably to tools.