1[40L-50L EXPANDABLE DESIGN]: The extra large carry on backpack with expandable feature gives you a spacious capacity experience. Normal state is 40L, dimensions are 20.1x12.6x8.7inch. after extended is 50L, dimensions are 20.1x12.6x11.8inch. You can expand the zipper and buckles according to your requirement 2[WATERPROO & DURABLE]: Travel backpack is made of water-repellent fabri and anti scratch material, effectively resist rainwater splashing, protect items from getting wet. The adjustable shoulder strap and backside with breathable mesh plentiful sponge pads can helps you relieve the stress from shoulder and back 3[CONVENIENT & PRACTICAL]: Business carry on backpack has external USB port with built in charging cable. offering you charge your electronic device by your own power bank any time and anywhere. there's a luggage strap makes it fixed on luggage for easier carrying. The hidden anti theft pocket on the back side can prot