Heat transference between layers (when camping)

[horizon]

This really belongs in the cycle camping section but it's a technical question and one for the physicists even if they don't camp:

So you're cycle camping and the night is cold. You have three insulating layers: your tent, your sleeping bag and your clothing (and indeed your mat, but that is included in all scenarios). Which of these three layers could or should usefully be increased the most in order to retain the most heat from your body?

[pwa]

A cap for your head. Max benefit for minimum material.

[Mike Sales]

A cap for your head. Max benefit for minimum material.

Absolutely. I was advised to wear a hat years ago when bivouacking on the Cuillin ridge and was glad of it. The head is a surprisingly large proportion of your surface area to leave uncovered, so a lot of heat can be lost from it.

[horizon]

So my question is, should you increase the insulation to the head or to the tent for instance or indeed to the bag if it covered the head (which some do). I accept we've increased from zero clothing regarding the head.

(BTW, I completely agree with the hat idea but I'm asking in this instance about the relative roles of the clothing, bag and tent.)

[whoof]

There are two elements to heat (also sound and light) transfer.Firstly, reflection and transmission at a boundary secondly insulation (absorption) through the material.

http://web.mit.edu/16.unified/www/FALL/ ... de133.html


The first requires a large difference in thermal properties at the boundary (which is why multiple layers are good as they provide multiple boundaries) the second high insulation material.
Tent fabric has neither property in great abundance. It would therefore depend on what your clothing and sleeping bag were made of, how many layers they consisted of and each layers thermal properties.

[PDQ Mobile]

The layer between you and the ground is usually much the thinnest. If the ground is cold it will sap heat.
I don't know how good the best inflatable mats are in this regard. I have stuck with Karrimat type foam because of size and wieght.

Upper covers can be added to and trap more air.
The covering of the head is wise advice.
Clothing is better used as insulation outside the bag.
A newspaper has many uses when camping, and is a surprisingly good insulator.

[julk]

My experience camping in the Uk is that an insulated sleeping mat makes a huge difference.
i moved to a down filled Exped mat (sadly £££) from foam mats and then self inflating mats.
Money well spent in my experience.

[Tigerbiten]

How warm a tent is comes back to it's design so is basically unalterable.
The closer the fly is to the ground all around then the better it traps warmer air in it.
But the better it traps the air, the worse the condensation will be on the inside of the fly.
Mesh panels on the inner are good when it hot but lets a lot of heat out to the fly when it's cold.
It will also be warmer if you can pitch your tent out of any wind.

Sleeping bags are more tricky.
A silk bag liner is warmer than a cotton one which is better than nothing.
The colder it get, the more likely you are to get water condensing on/in the bag which wrecks the insulation.
So the last thing you want to do in very cold weather is pull your head inside the bag so your breath cannot escape out.
A lot of heat can be/is lost through a full length zip so in very cold weather you can add a second bag inside the main bag with the zip on the other side.
Once it getter silly cold then a vapour layer inside the bag can be used to stop ice forming inside the outer layers of insulation, I did say "silly" cold .......
The trick of tumble drying a bag with a couple of tennis balls works well to "renovate" a bag by breaking up any clumps of insulation.

Luck .........

[NATURAL ANKLING]

Hi,
A sleeping bag is best at insulation gram for gram................but you do need a mat.
I would add insulation in the form of a sleeping bag................in a trade off against weight of a air filled mat compared with a closed cell mat.

So at -10 C pick your bag and matt..................but only a combined weight of 2KGs.
I wager that my bag will be heavier than most.................I will use a 18" x 72" X 9mm closed cell mat (350g).
You can include liners hats socks jim jams etc in that 2kgs.............I will still take the same two items above.
Ultralight air filled mats - one night with a failed mat would prove disastrous for most.

On tents you need to eliminate moving air from wind entering the sleeping area, to minimise the cooling of air in the sleeping compartment, and draughts on the sleeping bag..............that's why you need a heavier sleeping bag or bivy bag in the open.

A mummy sleeping bag means you don't need head gear / add a lightweight thin balaclava for comfort.
Head heat loss is proportional to surface area of skin.

Tent vs Bivvy Bag - ones more practical one is lighter at expense of condensation, sleeping only.
Tent vs Tarp - ones more practical one is marginally lighter at expense of exposure to elements, sleeping only.

On comfort - its down to what you can tolerate which is different for each individual.

https://www.ultralightoutdoorgear.co.uk ... list-i1401

Edited in red above for clarity.

[philsknees]

Some interesting figures on boosting performance to sleeping bags (admittedly at no little cost) using their products are quoted here:-
https://www.phdesigns.co.uk/combi-and-filler-bags
Well worth a browse even if the prices are now spectacularly high. They quantify performance boost figures for each of their overbags & filler bags and having owned one of their overbags for many years I've no reason to doubt them. They are probably the longest standing and most respected designer/manufacturers of high quality sleeping gear and know what they're talking about.
That said I now mainly camp in winter and strongly endorse the comments up-post concerning effective ground insulation and non-mesh tent inners.
One point not covered yet is the value of avoiding pitching on valley bottoms where the coldest air settles in winter. Selecting a site slightly up the valley side in near freezing weather can make a big difference to comfort.

[PH]

How warm a tent is comes back to it's design so is basically unalterable.

This, and the biggest design feature is size. Having gone from a tent with hardly any porch space to one with a similar overall footprint but much smaller inner the difference in temperature on a cold morning was very noticeable.

[PH]

Hi,
A sleeping bag is best at insulation gram for gram................but you do need a mat.
I would add insulation in the form of a sleeping bag................in a trade off against weight of a air filled mat.

I've come to the opposite conclusion, the bag underneath me offers very little insulation once the weight of of body has compressed it. It isn't all compressed of course, those hollows that get filled in all help to stop the air from moving around and taking your heat with it, but it's still carrying around lots of bag that isn't doing any good. The principle of an insulated air bed, is that it takes the insulation that would have been compressed and put it where it can't be. Gram for gram, I sleep warmer with a good insulated mat and a quilt than I would with a bag, though I've never tested this in severe conditions where it's possible other factors are present.

[PH]

Which of these three layers could or should usefully be increased the most in order to retain the most heat from your body?

I haven't done it but some swear by using a down jacket and a sleeping bag with less insulation in the top half. The principles are simple, it's your body producing the heat, keep it as close to you as possible, though you have to balance that with comfort. I take light PJ's camping, they're multi functional, add warmth, save getting dressed if I need to go outside at night, keep the quilt clean, and can in extreme weather be used as a base layer in the daytime.
You could ask the same question at home, you could heat the house, a room or put a jumper on, but you wouldn't expect your body heat to warm the house by much.

[horizon]

Really interesting replies from everyone - I'd like to respond later when I have more time.

[NATURAL ANKLING]

Hi,
A sleeping bag is best at insulation gram for gram................but you do need a mat.
I would add insulation in the form of a sleeping bag................in a trade off against weight of a air filled mat. compared with closed cell foam mat.

I've come to the opposite conclusion, the bag underneath me offers very little insulation once the weight of of body has compressed it. It isn't all compressed of course, those hollows that get filled in all help to stop the air from moving around and taking your heat with it, but it's still carrying around lots of bag that isn't doing any good. The principle of an insulated air bed, is that it takes the insulation that would have been compressed and put it where it can't be. Gram for gram, I sleep warmer with a good insulated mat and a quilt than I would with a bag, though I've never tested this in severe conditions where it's possible other factors are present.

Sorry I was not clear, see above in red, you do need a mat, even a thin non compressible is worth its weight.
Air filled to me mean a risk I don't want / need.

At a pinch in extreme I removed my outer clothing and used them as a mat, as I preferred that to wearing clothed in bag.
Debatable in at what limits including mass of bag this would be better?
I never wear clothes in bag not in bed.