Bushwalk Australia

I recently heard that the down in sleeping bags is more efficient at keeping you warm if you sleep down to your underwear. It needs to deflect radiant body heat?
Is this true? ...even on the coldest nights??? ...with a liner?

lyndoor

i have found that even on the coldest nights, im warmer in my sleeping bag if im nude rather than wearing thermals/clothing. if it gets too cold still, throw something over the top ov you on the outside of the bag

I would agree to an extent, although I tend to leave on a thermal layer if I'm cold. I've also found it pays to put a thermal beanie on. I've got very short hair most of the time, so this may be another factor. Apparently you lose quite a lot of heat from your head, so I guess this makes sense.

ollster wrote:I would agree to an extent, although I tend to leave on a thermal layer if I'm cold. I've also found it pays to put a thermal beanie on. I've got very short hair most of the time, so this may be another factor. Apparently you lose quite a lot of heat from your head, so I guess this makes sense.

To my surprise this may not be the case I am still sceptical tho, check this out.

http://www.healthline.com/blogs/exercis ... rough.html

C

Macca81 wrote:i have found that even on the coldest nights, im warmer in my sleeping bag if im nude rather than wearing thermals/clothing. if it gets too cold still, throw something over the top ov you on the outside of the bag

Macca81,
Don't you chuck your gear off at any opportunity anyway
c

G'Day
Down bags keep you warm by loft. Compressing the down greatly reduces this, that’s why you feel cold if you don’t have a good mat. Be careful what you put over you does not compress the down or you will be relying only on the warmth of what you put over yourself
Darren

lyndoor wrote:I recently heard that the down in sleeping bags is more efficient at keeping you warm if you sleep down to your underwear. It needs to deflect radiant body heat?
Is this true? ...even on the coldest nights??? ...with a liner?

lyndoor

Macca81 wrote:i have found that even on the coldest nights, im warmer in my sleeping bag if im nude rather than wearing thermals/clothing. if it gets too cold still, throw something over the top ov you on the outside of the bag

I have heard that it is supposed to be warmer to sleep in a down sleeping bag without clothes, I have been trying to find out if this is true or not for sometime now without success. My old fairydown bag (-10C rated) came with instructions that recomended to use light thermals and I have used this bag in snow at -18C while wearing several layers of thermals.

If anyone has some information that proves either way would be very intersted to read it.

Tony

corvus wrote:To my surprise this may not be the case I am still sceptical tho, check this out.

http://www.healthline.com/blogs/exercis ... rough.html

C

Good info - but I didn't mean that you lose the majority, just "quite a bit". Considering the surface area of the head, then if that article indicates around 20%, then proportionally it's fairly high.

Importantly, the article states "Head heat loss changes with how cold it is. The lower the temperature, the higher percentage head heat loss. Head heat loss is linear with temperature. At 0 degrees Centigrade, up to about 30 to 35% of heat could be lost through your head at rest."

So it becomes more important to keep your noggin warm the colder it gets!

ollster wrote:

corvus wrote:To my surprise this may not be the case I am still sceptical tho, check this out.

http://www.healthline.com/blogs/exercis ... rough.html

C

Good info - but I didn't mean that you lose the majority, just "quite a bit". Considering the surface area of the head, then if that article indicates around 20%, then proportionally it's fairly high.

Importantly, the article states "Head heat loss changes with how cold it is. The lower the temperature, the higher percentage head heat loss. Head heat loss is linear with temperature. At 0 degrees Centigrade, up to about 30 to 35% of heat could be lost through your head at rest."

So it becomes more important to keep your noggin warm the colder it gets!

...and the fact that when we dress up warmly, the head is often still uncovered (even when we DO put a beanie on, the face is still uncovered most times). I think that is one of the reasons people say we lose a lot of heat through our heads.

I'm currently bald (by choice - it happens occasionally), and am usually a bit of a cold fish (get very cold hands and feet), but if I feel my head with my cold hands, it always feels warm. I think this means that when the body is trying to conserve heat, it reduces the blood flow to some of the extremities (hands/feet), but not to the head, and therefore even when the body is actively trying to reduce heat loss in cold weather, it does not do this with the head. I guess this supports what you were saying.

Good observation Nik, I assume this is the effect that causes frostbite - conservation of body heat to the core and I guess the head.

The reason you can feel colder in thermals or other clothes at night is because they can restrict circulation through your limbs. Loose clothing is better, or no clothing and a liner. Whether your bag is down or synthetic is completely irrelevant.

The amount of body heat lost through radiation is tiny compared to other factors, and i doubt down reflects any radiant heat anyway.

As for the down needing to be at full loft to be useful, that's another bit of almost-but-not-quite truth. Down can be compressed by at least a factor of 2 and still maintain its full level of insulation. Beyond around 3x compression the insulation decreases, so the bits of your down sleeping bag that are directly underneath you don't contribute much insulation, but draping stuff over the top of the bag won't hurt.

As for the heat loss through the head, well, the body will always try to keep the brain supplied with blood in preference to the extremities, so if your feet are cold, put on a hat

Cheers,
Alliecat

I forgot to mention that I always wear a Hat for a sunscreen and a Beanie against cold and will do up my sleeping bag hood over my head and around my face if I feel it really cold .
Dont need experts to tell me how I feel at any given time ,just thought it may have been of interest to some
c

Son of a Beach wrote:

ollster wrote:

corvus wrote:To my surprise this may not be the case I am still sceptical tho, check this out.

http://www.healthline.com/blogs/exercis ... rough.html

C

I'm currently bald (by choice - it happens occasionally),

Did you get nits
c

Lol @ nits.

If you are really cold b4 you go to bed ,if possible do star jumps or windmill your arms it will get the blood flowing and heat your body up.
c

Based on my experince with a 750 gm top bag with no zip, I do not agree with this. If I am cold in my bag I put on a cocoon jacket and where light walking pants over my thermals. this makes me much more warm.

I can concur with the "add something over-top of your bag" comments.
Was sleeping under a veranda in Alice Springs in July last year (where you get 30 deg days and sub-zero nights), and while my nice down bag was rather cosy, was even more so once I had an extra blanket draped over top.
I suppose the concept is to trap layers of air that can decrease the rate of heat-transfer (a bit like a wetsuit will trap a layer of slightly warmer water against your skin).
A beanie on the head definitely helped too - but have realised that this needs to be quite loose - otherwise things get uncomfortable after a bit.

what about a bigger sleeping bag...and sharing body warmth with someone?

That's the go Strewth!

Otherwise, the way i see it, unless your sleeping bag is totally unsuitable, you feel the cold most when you first get in- You then feel it early morning around dawn, uncomfortable though unlikely dangerous. I tend to think that Corvus has the right idea. Warm up before you get in, that'll keep you warm until you get to sleep. I use thermals and drag a jacket in after me if it's really cold. Have heard the advice that sleeping with little on is the go but haven't seen much evidence.

Staying warm is a very personal thing. I have seen some people who are cold, no matter the bag rating once the temperature approaches 0* Even -9*c IS rated bags!

I share a bag with the missus! - well the two bags zip together anyhow.

Fairly warm, but gets a bit chilly when she has to make a pit stop in the middle of the night and unzips the bag...
I make up for it by eating baked beans for dinner.

As for the nude business - it's a myth.
Extra insulation INSIDE the bag decreases overall heat transfer to the outside, as long as you don't squash the down flat.

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I have found having something warm to eat before you go to bed helps generate some heat when you first get into a cold bag.
Also you can fill a platipus water bag up with hot water for a hot water bottle. Make sure the lid is on tight!
I think the key to not getting cold on those very cold days is to have your tent up and be in your sleeping bag cooking dinner as soon as possilbe to avoid cooling down too much after walking. I know some overseas long distance walkers time how long this takes to make this time as short as possible.

Thanks for the feedback, Guys, & clearing that up. Great discussion. I will take it all on board when I go camping in our chilly climate! Didn't think to use a hydrapak for a hottie! Good one!

lyndoor