Look at your classmates around you. You all wear the same uniform and similar sneakers. Do you want to stand out among them? A fashionable and useful backpack can be a great idea! Backpacks are lightweight and easy to carry. They are great tools for students. They help you to stay organized. You can keep school things, books and personal items like cell phones and keys neatly  . With a _ backpack, you can also stand out among your classmates. Tourists also love backpacks. With convenient backpacks, backpackers can move freely from one place to another. Meanwhile, they can also free their hands to do other things like taking photos. But in the very beginning backpacks were not what we see today. It is thought that US hiker Dick Kelty invented the first modern backpack in 1951. He used nylon   and aluminum tubing   to make backpacks lightweight. Then he added shoulder straps   and waist straps to transfer  much of the weight to the hips  . Today, backpacks come in different styles. Rolling   backpacks have wheels on the bottom. Users can pull them along the ground if they are too heavy to carry on their shoulders. And with more people bringing laptops to school and work, backpacks also offer space for lightweight electronics. In order to make the backpack light,   _   is used.
cotton nylon cloth paper