Interesting study about cold feet in a sleeping bag

[Matt Dirksen]

A few weeks ago, I stumbled across this 2016 NIH publication about supplemental heating inside of sleeping bags. I didn’t know if it had been brought up before so I thought I’d pass it on:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4725822/

While the introduction of supplemental heating to the extremities is not new to many of us, I found this statement somewhat alarming, when discussing the current sleeping bag testing methods:

”These studies indicated that the operating temperatures defined for sleeping bags provided insufficient protection at the body extremities.”

My take away: regardless of a bags temp rating, it’s a good idea to overcompensate for the hands & feet no matter what, since the testing methods don’t take “localized thermal comfort” into consideration.

(It appears my feet are saying “DUH” in this very moment)

Furthermore, if a bag company made a design which actually DID help the feet out, I’d never know it from the EN ratings. It would likely appear as a heavier bag to other bags with the same FP and temp rating.

[Dale Wambaugh]

Interesting. You would think that a design with extra loft at the feet would be easy and very marketable. Even doubling the down at the lower 12″ or so wouldn’t add much weight to a bag. Even quilts could be adapted that way. Personally, my head rarely gets cold, and generally tends to be too hot.

[Todd T]

Is this a surprise? I’ve always carried sleeping socks and gloves. The socks are more important than the gloves.

[Ken Thompson]

Down booties… Lighter than socks.

[Mark Fowler]

My feet are like furnaces.  Even if I am wearing my puffy under the quilt I usually have bare feet or at best a very light pair of socks.

[JCH]

>>Down booties… Lighter than socks.
Love my GFG down booties!  I prefer the bootie approach to bumping up the fill in the footbox as it makes the sleep system more adjustable.

>>My feet are like furnaces.
Lucky you…for sleeping anyway :)

[Tipi Walter]

The problem with feet on a winter trip is they just don’t start getting cold in the tent when it’s bed time—they often are cold hours before sleep when in camp doing camp chores or cathole visits or anything else.

When it’s bedtime they sit down in the footbox of the bag and remain cold and numb for several hours—no matter how low rated your sleeping bag is.

Last year for the first time I started carrying Hot Hands pouches and are used on bitterly cold nights and mornings when I need my hands and feet to function and stay warm.  For a typical 21 day winter trip I take about 6 two-pack pouches.  Once used they can be ripped open and the iron contents scattered in a firepit and the empty paper pouch burned.

My winter mantra is, “It’s All About the Hands and Feet” and this certainly holds true the older I get.  Warmth packets are a concession to advancing age.

[Paul Wagner]

Alpaca socks, purchases in a Street market in Peru for $5.  Amazing

[Jerry Adams]

If your body is a little short of enough heat to keep the core warm, then heat (blood) will be restricted to the feet and hands so they’ll get cold

My feet were a little cold so I wore booties, then I got a warmer sleeping bag and I didn’t need to wear the booties

Or, like they say, “if your feet are cold, put on a hat”

But wearing booties is a good solution too, maybe lighter than a heavier sleeping bag.

[d k]

“My feet are like furnaces”

Mine, on the other hand, are like small refrigeration units.

[Diane “Piper” Soini]

I have discovered the cure for being cold. It’s called menopause. It can be 20 degrees, my water bottles are freezing out in the vestibule, I’m shivering and my feet are frozen and then suddenly…! Emergency! Throw my sleeping bag off and relish the delight of the cool air against my skin. Then suddenly…! Emergency! Throw the sleeping bag back on before I freeze to death. Good times.

[Jenny A]

Diane, yeah…been there.  Mixed blessing!

Interestingly, one of the big selling points for many of the big name sleeping bag manufacturers for their womens’ bags is more insulation in the toebox and torso areas, since studies have supposedly shown that our extremities tend to lose heat more quickly when we get cold, which I interpret as keeping the babies alive and to heck with the carrier.  That’s well and good, but as others have commented, if your feet are already ice cubes when you get into a sleeping bag, you are just insulating ice cubes, not warming them.   I have successfully used the air-activated hotpocket things on occasion, but I prefer to jog in place or do jumping jacks before climbing into my bag for the night, just to get circulation going.  That helps as much as anything.

[D M]

Hot water in a bottle….SUCH luxury!! :-)) I’ve always been “popsicle toes”.

[Shane C]

I think hot bottle is the best option if you have the fuel to spare, I always carry a fresh hot hand pack for emergency but have never had to use one.

[steven w]

Dale Wambaugh is right, its easy(for manufactors) to add insulation to help problem areas but you are wrong if you think its not being done.

I saw the value in the idea when I last shopped for bags and bought a Nemo Disco which has added synthetic insulation in the toebox and uses water proof fabric there too. It was not the only choice in that respect but I wanted the room of the Disco’s spoon shape vs a mummy.

The idea is the extra insulation is placed around the down to reduce heat loss while preventing moisture from killing the loft and limiting that possible moisture intrusion with waterproof fabric. It works- most nights I go to sleep with cold feet I wake hours later needing to take my socks off because my feet are too hot.This has held true even on nights where I’m at the bags lower limit of comfort.

[David P]

Nothing ruins a nice nights sleep like ice cold feet. Like Jenny A suggested I do some running in place and swing my legs back and forth like a pendulum to get the blood going before jumping in the quilt.  I also use EE synthetic sidekicks booties and they are great!! I don’t use down anything, personally… Some folks get cold feet even with booties and I would suggest  wrapping the feet together in a spare warm layer like fleece or puffy (if you have a spare:o) )That way they get to share their warmth instead of being isolated in the booties.

@farwalker Hot water bottle sounds awesome and luxurious but I’ve never tried it. I’ve heard some wrap their wet socks around the bottle before bringing in the bag to dry them out. I just place mine next to my skin somewhere like shoulders or stomach…

the system in Steven w’s bag seems to be effective. It’s the same concept as layering a light synthetic quilt OVER your down quilt when in extremely cold temps. The moisture will get pushed through the warm down layer and condense on the colder, outer synthetic layer protecting the loft of the down. I layer a 40 degree Apex quilt over a 20 degree Apex quilt and have been toasty down to around -15F. Haven’t seen colder yet in use thankfully.

Mountain Laurel Designs also design their quilts with a higher loft from the waist down…

[Roger Caffin]

Nothing ruins a nice nights sleep like ice cold feet.

A very old and very reliable cure for cold feet: a warm head covering.
This is for real, but it seems that we have to keep repeating it. Hoodless bags and quilts are bad news without a warm head.

Cheers

[M B]

When my feet are cold putting booties on them doesn’t help them warm up… At all .

1. I learned this when I was a kid deer hunting. Once my fingers and feet get cold they do not self heat . appreciably. They need to be exposed to warm air warmed by the rest of my body.  For this reason booties and socks are of limited use. even after it’s warmed up outside and sun out, gloves would keep my fingers cold and keep them from warming. Same for insulated boots. To warm up I had to remove those things.

 

 

 

[Franco Darioli]

The brain has to remain within a degree or so to function correctly. So the heart will keep pumping warm blood to it in preference over the extremities.

(The average brain is about 3% of body mass but takes about 15% of the blood supply ).

Now if you don’t get warm blood into the feet, they will not produce heat . Socks can only slow heat loss , they can’t create heat by themselves.

Warm the head up and you will get warm blood to the extremities.

 

[Roger Caffin]

OK, the science behind it all.
If you get frostbite in your feet, you still survive.
If you get frostbite in your hands, you still survive.
If your torso gets much below 35 C, you are in some trouble but you can survive.
But if your head falls below 37 C (‘normal body temp’), you start to lose brain function, and your brain starts to fail.
Guess what your brain’s heating priorities are?

So yes, you can have frostbite on your extremities while your brain is still at 37 C – because your brain has shunted all available warm blood to itself. Your brain is extremely cold-sensitive and will cheerfully (I exaggerate only slightly) sacrifice your feet if necessary.

If your feet are ‘frozen’, it is no use putting down booties on them: there is little or no heat flow INTO your feet at that stage. You might of course be saying ‘but my head is still warm’, and you would probably be right. Your head is looking after itself.

The solution is to put some serious head covering on, to limit any heat loss from your head. Your head will get ‘too warm’, leading you to think you should bare your head. Don’t. At least, not until your brain has sent lots of nice warm blood down to your feet to warm them up. In serious cases of frostbite, the warming of your feet can even be a bit painful. That’s fine: it means your feet are recovering somewhat.

This is why I pour withering scorn on bags and quilts which do not have any hood. The lack of insulation around your head means you WILL have cold feet, overfill notwithstanding. If all you have is a hoodless bag or quilt, then get yourself a nice thick balaclava and WEAR it in bed. You can even get down-filled ‘balaclavas’ or hoods for really bad weather.

It follows then that just adding a balaclava may push your bag or quilt another 5 – 8 C lower in usefulness. My Katabatic down hood weighs 59 g and is probably overkill for anything in Australia. My synthetic hood (BPL Coccoon) is 56 g and more than adequate in Australia. Often we just use a fleece hood or ski cap. But normally we rely in a simple flap hood on our quilts.

This shows Sue with fleece ski cap and flap hood on UL summer-weight quilt in a single-skin tent. She took the fleece jacket off later. It was frosty outside.

Cheers

[Franco Darioli]

BTW, the above reminds me of a very peculiar condition called paradoxical undressing.

That is when with hypothermia right before the body gives up trying to keep the brain alive  it releases warm blood to the extremities. The sufferer than will strip off because he suddenly feels warm .

The reason why frozen bodies can be  found near naked next to a pile of clothing.

[David P]

So true roger! Sound advice. I live in a place where it’s negative 28-17 C everyday in winter. Neg 39 C was a low this year without wind chill. Neg 51 C with windchill. I know about warm hats… they are called bonnets where I am from Lol.  We lose a surprising amount of heat through our uncovered head, some studies say as much as 50%. There is not a lot of subcutaneous fat tissue in the head (for most of us) and the blood vessels don’t contract as much in response to cold like other parts of the body making the head very vulnerable to heat loss. When cold the body constricts superficial blood vessels in order to retain heat deeper in the core and vitals, in doing so it depletes blood supply to the extremities. This can make hands and feet feel cold even if they are well covered. Some people have poor circulation to begin with (Raynauds Syndrome) and this can affect them even more.

When running or working outside it’s amazing how much I can regulate my core temperature by simply removing or putting back on my hat.

personally I don’t get cold feet, but I wear up to four warm head coverings when sleeping outdoors. 1 warm hat, 2 insulated hoods, and synthetic balaclava. Depending on the nighttime temps. Sometimes my ski goggles for my eyeballs to keep from freezing.  My wimpy 40F hoodless quilt gets me down into the 20F range easily.

I am ready for spring, we are getting another 3-5 inches of snow today…

[Eric Blumensaadt]

My cold night sleeping bag preparations:

1. wear a light fleece balaclava (warm head, warm feet, as mentioned above)
2. put my zipped up WPB parka over the foot of the bag (slide it all the way on) and have the hood cinched down as well. This keeps condensation & melted frost from the tent’s waterproof floor “walls” off my bag and adds warmth to the foot area.
3. Lay pants and other day clothing under the mattress for some added insulation

[Winston W]

Is it unusual that I don’t like my feet warm compared to the rest of my body. For example I can’t sleep well it’s a blanket over my feet or socks on. When I was a child wearing those one piece pjs w the built it shoes, I wanted them cut off.

[Edward John M]

Sleeping at home my beloved often finds my feet out of the covers even tho I am snugged up deep in the doona with my head ensconced, but starting out with cold feet is another matter. I only wear sleeping socks in very cold weather but they often come off as I warm up

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