Polyamide (Nylon) plastic casings are the most commonly used in production of cooked sausages and hams such as luncheon meat and bologna. Polyamide casings come in two main varieties:  non-permeable and non-permeable. The non-permeable plastic sasuage casings are shrinkable casings and will shrink during the cooking process thereby reducing the water loss. Permeable polyamide casings remain the same diameter during the cooking process and thereby allow for expansion of the meat during cooking.