I have the Knack large backpack and wanted a water bottle that would fit the pocket without stretching it. My current bottle is 19oz which fit but was tight because of the cap at the top. The Knack bottle unsurprisingly fits perfectly in the pouch with no visible bulge on the outside of the bag. The bottle itself is well made and lightweight enough that I don't mind carrying it around at work to take it with me when I go to lunch.