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I was wondering how everyone prevents their drinking water from freezing while out in extremely cold conditions. I've read some methods online but wanted to know what peoples real experiences are with keeping their water warm.

For full disclosure I'm a design student with 4 years experience looking at creating a hydration product to be used specifically in below freezing conditions and would love to hear your thoughts!

It depends upon how cold it is and how long you are going to be out there. For single day drips of length less than 8 hours and down to -20F, but warming to 0ish, starting with a nalgene of boiling water and using an old thick wool sock to insulate it is all you need and is relatively light weight. This assumes of course, that the bottle is in your pack and your pack is next to you and your pack is car temp to start with. For longer trips I also bring a thermos for the very end of the day.

See here:

https://www.summitpost.org/cold-weather ... /346816/p2

I use OR water bottle cozies. If you are considering designing something, I would think a cozy using 25mm Evazotte foam would be the ticket. For hydration bladders you could make an envelope and tube from 6mm neoprene.

Colin Haley used bubble wrap to keep his bladders from freezing during his one day solo ascent of the North Buttress of Mt. Begguya in Alaska, which worked for him.

"Keeping it warm" and "keeping it from freezing" are two different things. Drinking barely-above-freezing water is awful.

In winter I'll carry two thermoses (REI type - you can pour without fully opening the screw cap) and I'll fill them with boiling water at the start of the day ( this means at home, if it's a day hike; at camp using a stove otherwise). When thirsty, I pour from a thermos into a cup ( thermos lid ) containing some snow. Adjust proportions as necessary so the water is a comfortable temperature for drinking. (Later in the day, as the water starts to cool, add less snow.)

A slim thermos will keep reasonably warm for around twelve hours unopened. If you're opening it once or twice an hour, it'll cool below body temperature within eight hours, but still resist freezing a few hours more. That's my recollection based on hikes in New England, temperatures in the teens F, thermoses kept in an outside backpack pocket.

The Thermos is a heck of a good invention. It's hard to improve on the insulating properties of a vacuum. The one improvement I can think of would be some kind of mechanism to minimize the cooling effect of the air that you have to let in as the water pours out. You'd have a downspout for the water to exit, and an air hole to replace the water volume poured out, but the air hole would lead to a separate chamber from the water, with an insulated membrane between the chambers. (In effect, the water chamber would be in a piston.) Building that kind of mechanism (cheaply) inside a vacuum thermos is a challenge left for the reader

Design students looking at this kind of problem (insulated coffee mugs are the typical example - very big market there) are always tempted by materials that change phase. In principle, you can store a lot more energy by melting something (wax is a good one - works at the temperatures you're interested in, isn't toxic...) than just by heating something up. In practice, the space and weight needed by your heat-storage element usually doesn't make a lot of sense in comparison to the amount of water you're trying to keep warm.

PS I haven't made the switch yet, but hydration bladders with bite valves are clearly gaining market share, starting with the military. I believe the state of the art for winter use is to blow air into the tube (against the weight of your pack!) after each use, clearing the tube of water so it doesn't freeze shut. There's got to be a way to improve on that.

6mm neoprene sleeve that the bladder slides into with a neoprene tube for the hose.

The "start with hot water/thermos" idea posted by Nartreb is the best idea if it's going to be below about 15, or windy. I also use the Outdoor Research water bottle coozie. I like how I can hang it from my pack for easy access. I have experimented with placing some chemical toe warmers inside the coozie but I can't tell if they really work very well.

Ah, why didn't I think of this:

portable radio-thermal generator

https://www.smbc-comics.com/comic/pu