There are two ways to buy one.
Unlined shells are the traditional setup. The leather is a windproof outer layer and you choose your own knit liner underneath. Pull the liner out to dry it overnight, swap to a heavier one when the temperature drops, wear the shell alone in milder weather. More work, more range, and the shell lasts years because the liner takes the sweat.
Lined mitts are one piece, ready to wear. Sherpa or Thinsulate is sewn in and you are done. Most people want this.
The leather matters more than the lining. Deerskin stays soft at low temperature while stiffer hides go rigid, so you keep enough hand movement to work a latch or a chain. Elkskin is thicker and takes abuse without losing much of that softness. Cow split is the toughest and the most affordable, and it is the right call if the mitts are going to meet bark, wire or steel.
On fit: order mitts a little loose. A trapped layer of air around your fingers is what holds heat, and a tight mitten cuts circulation and leaves you colder than a roomy one. If you are wearing a knit liner inside a shell, size up.
Every mitt below is cut and sewn from full hides, not panel scraps, and sizes run XXS through 3XL.
A chopper mitt is a leather mitten built for cold that gloves cannot handle. Your fingers sit together in one chamber and share heat instead of each one fighting the cold alone. That is the whole idea, and it is why loggers and farmers across Minnesota and Wisconsin have worn them for a hundred years.