Heavy duty cases are made from thick leather to provide maximum protection to your razor.
Cases are made from Chromium free vegetable tanned leather. This is much, much better for the environment and probably better for your razor as well.
Heavy duty safety razor cases are 1.9-2 oz, as opposed to 1.3-1.4 oz for the lighter cases. They are 5 inches long and 2 3/8 inches at the widest point.