The selection of the inner lining of the bag is also very important. What we pay attention to is a proper match. For example, the general polyester backpack and Pu backpack will choose the fine-grained polyester as the inner lining，like 210Ｄand 300D． Ｒeal leather bags，microfiber bags and even higher-end Pu bags will use cotton as the inner lining. There are also many backpacks that do not use lining directly, which requires the structure of the backpack to be very simple, and the internal stitching line to be simple, otherwise there will be a lot of internal lines visible, which is not look nice. There are also Pu bags or real leather bags, use the same PU or leather as the inlay and outside fabric, which shows a high-level sense. The inlay PU or leather needs to be thin PU leather or real leather, such as pigskin.