I use an Eberlestock J104 backpack which has an integral compartment for the hydration bladder (made by source) this does not allow me much flexibility to carry the pack inside my jacket. I have been trying to come up with a way to keep just the hose from freezing by tucking it inside, but it is such a pain to dig out to take a drink that it takes away from any benefit that may be gained. Imagine what happens if the stupid thing were to leak inside your jacket when it’s -25 deg cel or below. On my next trip I will see what works best, a wide mouth Nalgene bottle or my army issued 2L collapsible canteen with insulated carrier. I will let everyone know what the better of the two was.