I hope you will like our products. We guarantee 100% quality and brand new. This backpack needs to absorb light in the daytime and shine at night. The longer the backpack absorbs light,The longer the backpack in the dark glow time. All the goods in our shop are shipped by China. Buyers after placing the order ,within 24hours arrange send it .Support for global transportation,Absolute guarantee customer satisfaction. Size: backpack :45*31*16cm *How to make it blue. 1.This backpack needs to absorb light in the daytime and shine at dark. 2.The longer the backpack absorbs light,The longer the backpack in the dark glow time. 3.You need to carry it in the sun for some time.And then walk to the dark place. 4.Then it will be glow blue. *If you want to use External USB Charge Function, you have to do as follows: 1.Buy a mobile power 2.Connect your mobile power with the USB interface inside the backpack 3.Connect your phone with the USB interface outside the backpack 4.Charging begins. Backpack Usage: travel, hiking, school, Casual daypack, City backpack, laptop / iPad backpack etc.It's super good for travel ,work or school. Main Material: high quality strong oxford canvas Package :1 x Fashion Travel luminous Backpack.Buying BTS series backpacks may get random BTS postcards Backpack style and color to picture prevail£¡ *Kindly Reminder: 1.the has the high grade canvas material is soft and wear resistance. 2.two-way zip that is comfortable to use. can relieve 3.the comfortable and adjustable shoulder straps , so protect that shoulders on her. 4.the has a large capacity. so they can easily with your ipad, a4 - file, magazine and other everyday things. 5.Please allow 1-3CM error due to manual measurement. 6.The colors may have different as the difference display,pls understand.