How to protect your down in case of a punctured hot water bottle/bladder.

I've always felt like the hot water bladder in the bag/quilt is just a bad idea. I've read too many accounts over the years (and seen it first hand a few times) to even want to try it. In the end, it just seems like a better idea to bring more down sleepwear or get a warmer quilt/bag. That's my 2 cents anyhow.

I'm a bit leery of regularly using hot water bottles in bed. This is the kind of thing that is frequently touted in Backpacker Magazine as an experts tip for anytime it gets slightly cold out.

My opinion is that if you're using this strategy regularly, then you ought to be carrying a warmer bag. When you consider the weight of fuel that you're burning (if done nightly) plus the hassle, it may be lighter and safer just to bring a toastier bag. Hot water bottles also don't stay warm that long, even when wrapped. Yeah they help you fall asleep but it's still a patch solution and a somewhat clumsy one at that.

So I suggest almost never using this technique, and if you do find the occasion to employ it, then grab a second waterproof layer to double bag the water bottle. I use a cuben dry sack for my down sleeping bag anyways, so I could repurpose that at night. If you've got a trash compacter bag, or silnylon stuff sack you could use that. In a real pinch, you could use your rain jacket (tie the sleeves shut etc).

Hot water bottle will keep you warm at beginning of night

My problem is towards end of night, when it gets coldest and my metabolism has slowed down. Hot water bottle doesn't do much at that point.

Its a luxury and a nice psychological tweak. Like Jerry said, it's not much use at 3AM. If you're wearing socks, it's not like your feet will contact cold nylon when you first get in. With the use of Sawyer Mini filters, more of us may be curling up with a filter in a bag to keep it from freezing, but a freezer grade ziplock should take car of that.

LDPE and HDPE Nalgene bottles are a couple ounces lighter than the Tritan plastic versions.

The Nalgene Oasis canteen weighs 4.6oz and holds a liter. The canteen shape would stay put better and be more foot friendly. They are easier to grasp and drink from and carry well in a side pocket with a lower center of gravity. They have become my go to water container.

I think a hot water bottle is a great way to heat up a sleeping bag but it seems that once the water drops below 98.6*f, it will start to conduct heat away. Thoughts?

In general, I would never put a hot water bottle into my down sleeping bag. In winter, I do put a cold water bottle in there, but that is only to keep it from freezing. Lukewarm water is a lot easier to deal with for morning cooking.

The one exception to this would be if we had one person who was going hypothermic. By definition, that person can't maintain body temperature, so they no longer have the ability to warm up their own sleeping bag. A hot water bottle would be one tool to get a warm night started safely.

–B.G.–

"it seems that once the water drops below 98.6*f, it will start to conduct heat away"

I think that's correct.

"The one exception to this would be if we had one person who was going hypothermic"

That is a totally different case. Hot water bottle would be good then. Or, better yet, drink it. But I think if you warm up too quickly, the body will release cold blood from extremeties which will make things worse?

Put it in to a dry bag.

"That is a totally different case. Hot water bottle would be good then. Or, better yet, drink it. But I think if you warm up too quickly, the body will release cold blood from extremeties which will make things worse?"

If a person is going hypothermic, then that is a lot different from somebody who is already deeply hypothermic. The deeply hypothermic patient is very fragile, and you don't want to do anything abrupt in the rewarming process. Often the body has minimized circulation to the extremities, and you don't want to get that going very fast. The penalties can include cardiac arrest. On the other hand, if somebody is going hypothermic, then some moderate actions to rewarm them will be necessary. An hour in a sleeping bag with a hot water bottle can do wonders.

–B.G.–

sure you need to make sure the top is on properly, but who here has direct experience with a nalgene bottle rupturing in yours or somebody you were with sleeping bag. when it's cold you need to warm your sleeping bag one way or another. i'd prefer to use the energy stored in a hot water bottle instead of the energy stored in me, which i can use late in the night to keep warm. it also helps to nibble on a snickers bar or the like before bed for some extra bedtime fuel. as far as fuel waste goes, i'd need to melt snow in the morning anyway, so the bottle(s) is a head start. also, there's something psychologically comforting about climbing into a warm sleeping bag and feeling the warmth from a water bottle.

i make sure my bottle top is on properly and wouldn't use a water bladder or gatorade style bottle for the same purpose. that's how i protect my down bag.

When I go to bed, my metabolism is higher because I've been walking around and stuff. And the air temperature is warmer. No problem being warm. I start with the sleeping bag open and maybe hat off, then after an hour I'll start "battening down the hatches". Having extra heat then will make no difference, it will just delay closing up sleeping bag and donning hat and other reserve insulation.

If you're sleeping and cold, your metabolism will probably be raised to keep you warm? This will deplete your reserves so you won't be able to use them later in the night? I can see how the warm bottle may help in some cases.

"it seems that once the water drops below 98.6*f, it will start to conduct heat away"
1) 98.6 F is core body temperature but extremities like feet are much cooler. The thermoneutral point would be maybe 80F if it's at your feet, depending on what your body is doing.

2) To get cooler than your body, a bottle would have to give off that heat. Heat would not be given off if the surroundings were warmer than the bottle – rather heat would be flowing in. So actually the bottle will cool and give off heat until it's at an equilibrium with the surrounding temperatures and then it'll be pretty much stable unless you've got half the bottle poking out of your bag and wicking away heat. So it reaches an equilibrium with your body and then its fairly irrelevant unless it has the ability to conduct its heat away somehow.

One downside is that if your feet were made cool somehow (ie. your body shuts of circulation for a bit) then the bottle could cool more. If your body then tried to warm up your feet it would be harder to do so because it would need to warm the bottle also in this case.

Somewhat on this topic is the oft repeated claim that peeing at night will keep you warmer because it takes energy to keep the pee warm. I see this everywhere including Backpacker magazine and it's totally wrong. I agree one should go pee – but only because it's tough to sleep with a full bladder. It does not take more energy to retain that pee.

The bladder is deep inside the torso – nicely tucked into the pelvic girdle. It can only gain heat from your body and similarly can only lose heat to your body (when you're not peeing). The bladder can't magically conduct your heat into the outdoors. Yes it takes heat to warm urine (assuming you aren't drinking hot water), but warming urine is unavoidable and it does not take heat to keep it warm.

Imagine a bladder filled with urine at core temperature (unavoidable). Heat would not flow into the bladder because it's at the same temperature as your guts. If somehow it did, then the bladder would be hotter than your guts so the heat would flow back out – thus it's a wash. Any heat the bladder is "losing" is being lost to you. Any heat the bladder is gaining is coming from you. It's entirely neutral and not a continual sink for energy.

If you really dive into the nitty gritty details of it, it's actually more heat efficient to have a full bladder. The added mass buffers swings in your body temperature (to an extremely small degree), which causes a slight reduction in heat loss because it's more efficient to be at a constant temperature than a fluctuating one.

I've measured torso skin temperature at 92 F, legs at 80 F like you said.

I suppose if you got up to pee, you would lose some heat because you'de be out in the air for a bit where it's much colder, warm air inside the sleeping bag would be lost, but your metabolism would increase a little from walking around so maybe it's a wash. Main thing is, if you got to pee, you got to pee, then you'll be more comfortable.

I agree, removing urine won't make any difference, it's inside you. I suppose your surface area would decrease a negligible amount, which would make a negligible difference in keeping warm.