Casing (sausage)
（重定向自Natural casing）
Casing, sausage casing, or sausage skin is the material that encloses the filling of a sausage. Casings are divided into two categories, natural and artificial. Artificial casings, such as collagen, cellulose, plastic, and extruded casings, are relatively new to the field, mainly borne of market demand during the technological advances of the early 20th century.