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All the hiking gear is getting more and more lightweight and hi-tech... but vacuum flasks haven't changed much for the last fifty years, they're still extremely heavy pieces of steel! One litre bottle weighs 600-700 grams...

Generally I try to avoid using vacuum flasks, but there're some conditions when they're indispensable (winter hiking in restricted NP where you can't use any kind of stove, for example).

Using an insulated bottle (not a vacuum flask) is not enough; in fact, sometimes even the vacuum flasks get cold(-ish) by the end of a long winter day in the mountains!

I tried using flameless heaters but their temperature drops down significantly in winter (on one trip in balmy 32F/0C a heater made my tea just barely lukewarm!)

Is there any better/lighter way to carry hot liquids on such trips?

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  • Is a carrying a very light-weight burner, e.g. for Esbit tablets, an option? – phipsgabler Feb 9 at 13:06
  • Nope @phipsgabler, because in such national parks any kind of flame is strictly forbidden... Moreover, even when I'm in a place where I can use a stove, there's cold+wind+no time to stop and wait for the water to heat/boil... I'm talking about day hiking, not sleeping overnight, in that case you can usually find a way/time to cook. – Alexander Feb 9 at 14:02
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    50 years ago vacuum flasks were almost always glass instead of steel (2 layers of glass containing the vacuum, inside a protective housing). They were a little lighter if the housing was plastic but much more fragile. – Chris H Feb 9 at 14:57
  • Ha @ChrisH that's right :) I remember those flasks actually... maybe if I can find an old one, that would be a solution?! – Alexander Feb 10 at 12:16
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    "winter hiking in restricted NP where you can't use any kind of stove, for example" - I find this claim hard to believe. Even in "extreme" fire danger danger situations backpacking stoves are permitted in parks that I know of, and I could not find a park with such a restriction. Can you let me know what parks you are dealing with where said restrictions exist? – whatsisname Feb 11 at 2:39
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A smaller flask is of course lighter, but loses heat faster and holds less. Your whole drink strategy needs to be considered.

A litre is a lot though, unless sharing - there's plenty of choice of 500-600ml flasks; one I found easily weighs 300g (compared to 530g for their lightweight 1l model. Thermos, the brand I've linked, has been in the business a long time (since the vacuum part was always silvered glass, visible on the inside) and is synonymous with vacuum flasks in the UK. I wouldn't go smaller than about 500ml as the hold time tends to be too short.

The main loss is at the lid, which is merely insulated. A better quality flask will hold heat better (and may weigh a little less overall). The best lids I've found are those that allow you to unscrew slightly to pour, using all their volume for insulation. I would avoid those with a clever mechanism that traps the dregs of your drink in an inaccessible volume. This means less insulation and also, having opened one up destructively, I never want to drink from anything so filthy again. Regardless of the lid design, supplementing the insulation in this area (wrap it in spare clothing, use an insulated pouch, etc.) will help a bit.

The smaller the flask, the more important it is to preheat it well when you fill it (the surface area to volume ratio is worse, and the steel is the same thickness, so each drop of your drink is heating more steel).

The other important heat loss is opening the flask, letting out hot drink/air/steam and replacing it with cold air. Waiting as long as possible for the first drink helps here. If you're in a group, share out one flask at each stop, keeping the others closed. I'll sometimes save mine until we're nearly done, a habit from winter kayaking when a hot drink borders on being emergency kit if someone gets wet and cold.

Hiking I might be tempted to carry a tiny stove (you could do better than this 60g one I made) for actual emergencies, combined with a smaller flask (and a water bottle, possibly insulated), or, if you drive to your hike, leave a big flask in the car for the end - something else I've done when kayaking.

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  • What does this bit mean? This means less insulation and also, having op in proportion ened one up destructively, I think autocorrect has come to your "rescue" and made some words not be the right ones. Possibly along the lines of "opened one up destructively"? – bob1 Feb 9 at 19:48
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    @bob1 thanks, I'll fix it in a minute when I've got the PC on. Your interpretation is right but I can't blame autocorrect here - I've inserted " in proportion " in the middle of "opened" instead of where it was meant to go – Chris H Feb 9 at 20:03

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