1.you can pull the tail of the zipper, straighten the zipper, and then pull it up and down repeatedly to check whether it is smooth. If it is not smooth, it is often because the zipper is stuck with other things, so it is not smooth. You need to remove the obstacles to get back to normal. 2. The simplest and most effective method is to coat the surface of the zipper with a layer of wax and use the lubricating effect of the wax to achieve a smooth effect. After wiping back and forth with a candle on the surface of the zipper, and then repeatedly pulling it from bottom to top several times, the zipper is smooth.
3. In addition to wax, you can also use lubricating oil. You should pick a more transparent and clean one. After dropping a few drops on the position of the zipper pull ring, you can pull it several times to achieve a smooth goal.
Of course, you still need to find a reliable supplier to buy a backpack or custom backpack. Why not try upbag?