The structure of the back of a backpack directly determines its purpose and grade. The back structure of a famous brand computer backpack is more complex, with at least six pieces of pearl cotton or EVA as a breathable cushion, and sometimes even an aluminum frame. In contrast, the back of a general backpack is made of a single piece of pearl cotton about 3mm thick as a breathable board. The simplest drawstring backpacks do not have any padding material except for the backpack material itself. Computer backpacks are of higher quality but have fewer styles, while sports backpacks have many styles but average materials and workmanship. Fashionable backpacks have a small capacity and are suitable for ladies to use on informal occasions.