Flexible capacity - Shrink it to a handy tiny 200ml ball shape, or expand to the full 550ml. Size is perfect for both kids & adults. The travel water bottle is foldable which saves about 50% of space for outdoor activities. Easily squeeze. Very handy to carry around. Great bottle for school, collapses down in size to store in school bag at the end of the day. The hiking water bottle also comes with a carabiner for you to clip onto a backpack for school sports, traveling, gym.