Casings are usually divided into natural casings and artificial casings. Natural casings mainly use the longest intestines in animal viscera. Now sheep intestines are usually used, so they are also called sheep intestines, and pig intestines are called pig intestines. In the past, cattle intestines and horse intestines were used as casings. Natural casings are characterized by good air permeability, so after properly drying the goods, smoke them. The smoke components are attached to the goods to get our favorite flavor, and the casings can be eaten directly. Artificial casings are divided into breathable casings and non breathable casings. Breathable casing can be divided into edible casing and non edible casing. Edible casing takes animal skin as material, and its properties are similar to natural casing. We call it collagen casing, which is characterized by air permeability and edible. Non edible casings mainly include cellulose casings and cellophane. Cellulose casings can be divided into cellulose casings and fibrous casings. This kind of casings is characterized by air permeability but not edible. Today, there is also a non edible casing made of plastic. This casing also has air permeability and can be smoked, so it is called smokeable plastic casing. Non breathable casings are mainly plastic casings. According to different data, they can be divided into polyvinylidene chloride (PVDC) casings and nylon casings. According to different shapes, they can be divided into sheet casings and cylindrical casings. This kind of casing has many kinds of standards, can be printed, easy to use, bright and beautiful, and is suitable for cooking goods.