WH, you could fill it and chuck it in a pack no worries, kind if like a soft wobbly water bottle
They do not have a drinking tube like the bladders, so you have to take the bag out to drink or dispense water, but they are a hell of a lot tougher than the plastic bladders. I've had one strapped to the outside of a pack, and it got scuffed up etc, no leaks.
What is nice as well is that they have a huge threaded filling cap (bomb-proof thread), and a small flip-up spout. Have a look on youtube, should have some reviews etc.
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