The butterfly dress, known as the "Butterfly Bag", is an early album. It appears in the fold and evolves from the fold. It appeared at the end of the Five Dynasties and prevailed in the Song Dynasty. The method of loading a butterfly is to insert the page along the indirect seam. Fold the printed text inward and align the book with the crease. Use a bag of backing paper on the back of the crease and finally cut it into a book. It looks like the wings of a butterfly flying, hence the name "Butterfly." The book's binding form has evolved into a butterfly costume, which indicates that the binding form of Chinese books has entered the "album" stage. The binding form that began to appear in the late Song Dynasty - the back backpack of the bag is also known as the backpack. It is a form of binding based on the development of a butterfly dress. It appeared at the end of the Southern Song Dynasty. It is used more in the Yuan, Ming and Qing dynasties. The "Yongle Grand Code" of the Ming Dynasty and the "Siku Quanshu" of the Qing Dynasty are binding. The main difference between a backpack and a butterfly bag is that when the page is folded, the core faces outward and the back faces in opposite directions. When turning pages, each page is in front. The binding method is fold alignment, the outer wear and wear of the right column. The form of the frame that prevailed after the middle of the Ming Dynasty - the same is true for the folding of the wire and the backpack, with the heart facing outwards and the back facing opposite. The difference is that the backpack consists of two separate covers, the back of the bag changes to the back, and the perforations of the paper become lines. This line is a Chinese tradition. This is the most advanced book in the history of binding technology. Wired books are easy to read and not easy to break. The craftsmanship and book style of wire-bound books have changed to varying degrees, such as "wrapped corners" and "robes", but they do not exceed the line load range.