Much like a jacket, Mitts or Mittens are made up of several components that help keep you protected, dry, and warm. These are the shell material, membrane, insulation, lining, and palm.
A proper fitting Mitt should fit snugly and allow enough room at the end of outstretched fingers for you to pinch about a quarter of an inch of fabric.
Make sure your palm is completely inside the cuff so your wrist remains covered. When you make a fist, the fit shouldn’t be so tight that is constricts your fingers from curving fully