It can also be divided into cellulose casings and fibrous casings, which are composed of natural fibers such as cotton wool, wood shavings, flax, and other plant fibers. They cannot shrink with meat filling and are not edible. They can be used as packaging for large and small red sausages, such as the outer packaging of ham sausages. The characteristic of this type of casing is that it is breathable but not edible. It has good toughness and breathability, and is also stable during rapid heat treatment. It can be smoked and colored even in wet conditions.