1, gas expansion: cold noodle soup contains gas, such as carbon dioxide. Cold noodle soup is sealed in the bag, and the gas can't escape, which causes the bag to expand.

2, bacteria gas production: there are bacteria in the cold noodle soup, these bacteria will produce gas when metabolized in the soup, causing the bag to expand.

3, packaging problems: problems in the packaging process, the bag is not tightly sealed or defective, resulting in gas entering the bag. Cold noodles are traditional Korean folk pasta. Among them, soba noodles are famous for their cold noodles.