Sleeping bag liners

24 Apr 2013 13:43 - 24 Apr 2013 15:37 #56753 by plouw
Replied by plouw on topic Sleeping bag liners
@Ghaznavid: this sleeping naked in a sleeping bag still doesn't make sense to me, i tend to agree with this guy: http://http://sectionhiker.com/sleeping-naked-in-a-sleeping-bag/

I believe the only thing that works in the cold is layers. I would rather put my trust in four layers of non technical clothing than one layer of technical gear. (unless it is raining ofcourse)
For instance, if you are wearing an outer shell (jacket) and you are still cold, you put more layers on underneath this. Surely a sleeping bag is no different. I don't know, just how i interpret it.
Last edit: 24 Apr 2013 15:37 by intrepid. Reason: fixed link

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24 Apr 2013 14:50 - 24 Apr 2013 14:51 #56754 by JonWells
Replied by JonWells on topic Sleeping bag liners
There really seems to be no definitive answer to this debate so far. I do remember once reading an answer from a physicist who stated something along the line of

"An object with MORE insulation cannot cool more rapidly than an object with LESS insulation."

I would dearly love for Mythbusters to settle this matter:

2 X Identical sleeping bags
2 X Identical life sized dummies at 37°C, one heavily clothed, one lightly clothed

Both would have temperature sensors in their cores, and their rate of cooling can be precisely monitored and the debate would end once and for all.

Perhaps I should mail them... :whistle:
Last edit: 24 Apr 2013 14:51 by JonWells.

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24 Apr 2013 16:46 #56755 by ghaznavid
Replied by ghaznavid on topic Sleeping bag liners

Now suppose you’ve taken all these steps and your are still cold. Well, now is the time to start putting on clothes. Start with long underwear, socks, and then a coat with additional insulation. All of these will descrease the amount of room in your sleeping bag taken up by air and increase your warmth level because your body has to heat less air in the sleeping bag around you. If you are still freezing, you can stuff more of your gear inside the bag with you, to further reduce the amount of air in sleeping bag.


His assumption on the space there is rather flawed - when you sleep in a sleeping bag, all the material directly above you sits on you (thus that part would make no difference), but unless you have a massive volume of clothing on you will never fill the parts next to you on either side, by your feet etc.

plouw wrote: I believe the only thing that works in the cold is layers. I would rather put my trust in four layers of non technical clothing than one layer of technical gear. (unless it is raining ofcourse)
For instance, if you are wearing an outer shell (jacket) and you are still cold, you put more layers on underneath this. Surely a sleeping bag is no different. I don't know, just how i interpret it.


I felt the same way for ages, and its possible that different bags work differently in this regard. However, my experience on my -7 Mountain Hardware Pinole is this:
- Night before GT I sleep in lots of clothes and am cold at Silverstreams in my tent
- Night 1 on GT above Isicutula Pass I sleep in lots of clothes and am cold again (but the weather is fairly warm)
- Day 2 I complain about how useless my bag is. Tony tells me how Mountain Hardware is a good brand, my tent mate tells me that her MH -15 bag held up perfectly on Aconcagua (6900+m). Tony tells me to try sleeping in less clothing.
- Night 2 I try what Tony suggested and am really warm - I never look back on this. I wake up to find my tent covered in snow
- Night 3 I get into my tent pitched on snow. I'm cold, wet and miserable - yet I am warmer than I was on the first 2 nights

To me that is definitely conclusive.

The reason I brought up aerogel vs a non-foam air mattress was simple - aerogel is the best insinuator known to man, yet a plain air mattress usually has an R-rating under 2. The only difference is that aerogel basically prevents heat transfer by convection while in air most transfer is via convection thus accelerating heat loss close to the person.

JonWells wrote: I do remember once reading an answer from a physicist who stated something along the line of

"An object with MORE insulation cannot cool more rapidly than an object with LESS insulation."


I disagree. Take this example: put your clothes on in this order: raincoat first, then your fleece and then your thermal inners on the outside. You have exactly the same ingredients, but the result would be substantially different (assume its not raining or anything).

JonWells wrote: Both would have temperature sensors in their cores, and their rate of cooling can be precisely monitored and the debate would end once and for all.

Perhaps I should mail them... :whistle:


Not a bad idea - if we all mail them they might think its a widely asked question. I would also be interested to see the test results :thumbsup:

Getting to the top is nothing, the way you do it is everything – Royal Robins
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24 Apr 2013 16:49 #56756 by ghaznavid
Replied by ghaznavid on topic Sleeping bag liners

Getting to the top is nothing, the way you do it is everything – Royal Robins

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24 Apr 2013 16:57 #56757 by ghaznavid
Replied by ghaznavid on topic Sleeping bag liners
My post on the Mythbusters submit a myth page:

ghaznavid wrote: The sleeping bag myth:

It is warmer to sleep in a sleeping bag without clothes on than it is with clothes on.

The logic:

when not clothed the air between the hiker and the sleeping bag is warmed by convection of radiated heat, thus heating up the down in the sleeping bag and making best use of the bag design.

When heavily clothed in technical thermal clothing, the clothes (which are usually a bit tight) hold a fair amount of heat and only allow the balance of the heat to escape to the space between the clothed human and the bag. The air "mixes" (heat transfer via convection) with the cold air inside the bag, thus preventing the down from taking and heat and thus making your sleeping bag an expensive paper weight.


Getting to the top is nothing, the way you do it is everything – Royal Robins
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25 Apr 2013 06:17 #56763 by Josh of the Bushveld
Nice!
I'm reserving opinion on the subject (from a theoretical point of view).
I'll try do more field testing/experimenting in the future.

I made my second liner yesterday from lighter-weight fleece. Unfortunately it weighs around 460g which isn't as light as I wanted it.

I had a design idea though, to make a liner with 2 different weights of fleece, the thicker, heavier, warmer fleece on the bottom and the lighter fleece on top, the thinking being that the warmer fleece on the bottom would help compensate for some of the lost insulation due to the sleeping bag being compressed.

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25 Apr 2013 06:27 #56764 by plouw
Replied by plouw on topic Sleeping bag liners
i once cuddled my emergency blanket inside my sleeping bag, that was the warmest sleep ever.
@joshilewis: maybe try and incorporate a sort of foil into your liner?

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25 Apr 2013 06:36 #56765 by Josh of the Bushveld
@plouw: its an interested idea. I did some reading on vapour barrier liners yesterday, very interesting technology. I'm not sure how good a fit it is with the conditions in SA though, don't know if it gets cold enough etc.

I'm also looking at buying (or trying to make my own) silk liner. Seems they can't be beat for the weight (and volume).

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25 Apr 2013 06:41 #56766 by ghaznavid
Replied by ghaznavid on topic Sleeping bag liners

joshilewis wrote: I'm also looking at buying (or trying to make my own) silk liner. Seems they can't be beat for the weight (and volume).


I was wondering about silk liners - if you have any luck, please let me know.

@Plouw: emergency blankets don't breathe, that's the only reason they aren't usually used. The Messner brothers survived an emergency bivy at 8000m on Nanga Parbat with just the clothes they had on and an emergency blanket - so they definitely work. The issue I see with incorporating it into a bag is that it tears easy and is hard to sew into place. Although I have put one under my tent when it is wet/snowy, its worked really well all 3 times.

Getting to the top is nothing, the way you do it is everything – Royal Robins

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25 Apr 2013 06:58 - 25 Apr 2013 07:01 #56768 by Josh of the Bushveld

ghaznavid wrote:

joshilewis wrote: I'm also looking at buying (or trying to make my own) silk liner. Seems they can't be beat for the weight (and volume).


I was wondering about silk liners - if you have any luck, please let me know.

Will do.

At the moment I'm looking at these:
Cocoon Silk MummyLiner (Can get for $50 on Amazon )
Silk liner on Mountain Mail Order

I'm not so confident that I'll find 100% silk fabric in Jo'burg
Last edit: 25 Apr 2013 07:01 by Josh of the Bushveld.

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