Reflective Inner Tent Surfaces for Cold Weather

[Leo L.]

Leo, you wrote: "So assuming all radiant heat is emitted off the outer surface of the bag, its important to know the temp of this outer surface."
I was thinking, that the sleeping bag didn't matter, when it comes to radiation, but, if the sleeping bag is absorbing some of the radiation from the skin, it will also radiate back to the skin at a higher rate than usual, according to it's radiation properties.

mekineer,

The bag's outside temperature is low, quite close to the air temp in the tent. Thats the personal experience by touching it.
I believe in reality the bag (all its layers put together) is "radiation-proof", and there is no heat transfer from the body to the tent by radiation straight through the bag, but only by convection and by breathing vapor-loaden air (maybe very little by radiation from one layer inside the bag to the next).
Why do I believe this?
Because, when (assuming) the total heat loss of a human body from inside the bag is, say, 1/3 by radiation 1/3 by convection and 1/3 by evaporation, why dont all bag manufacturers focus on all 3 items?
They focus on convection the most, a little on Evaporation (for very extreme conditions), but they leave the radiation aside.
Do you really believe, all bag manufacturers around the world are so stupid to overlook any significant heat loss by radiation? No, I dont believe so.
We had sleeping bags in the past that had a perforated space blanket inside, and were advertised as being very "warm" by having very low weight.
Total crap. Didn't work when they were new, and didn't work when they were used, exept the space foil had crumbeled to pieces soon and thus provided some quiet sleep.

So this leads me to the conclusion that a typical (down) bag blocks direct heat Radiation, and all that counts in the total heat transfer is convection and radiation off the outer surface of the bag (plus some evaporation).

[gravityman]

I agree, down and nylon are not transparent to thermal radiation.

The material will absorb the radiation and then re-radiate. As has been said, the outer layer of the nylon is cool, the down is doing its job, and there isn't much to be gained by a reflective layer above you.

Below you is a different story, where you are conductivity coupled to the mat below you. Previously, large tube pads cause a lot of convective losses, however, by using a radiative barrier in the NeoAir, they have overcome this.

[Tipi Walter]

All of this analysis (root Latin word: anal) can be dispensed with by taking this tent and sleeping out in the backyard for two weeks. If it doesn't rain set up a water hose with a sprinkler over the tent. Saturate thruout the night. Then repeat in December.

[Starchild]

mekineer,

The bag's outside temperature is low, quite close to the air temp in the tent. Thats the personal experience by touching it.
I believe in reality the bag (all its layers put together) is "radiation-proof", and there is no heat transfer from the body to the tent by radiation straight through the bag, but only by convection and by breathing vapor-loaden air (maybe very little by radiation from one layer inside the bag to the next).
Why do I believe this?
Because, when (assuming) the total heat loss of a human body from inside the bag is, say, 1/3 by radiation 1/3 by convection and 1/3 by evaporation, why dont all bag manufacturers focus on all 3 items?
They focus on convection the most, a little on Evaporation (for very extreme conditions), but they leave the radiation aside.
Do you really believe, all bag manufacturers around the world are so stupid to overlook any significant heat loss by radiation? No, I dont believe so.
We had sleeping bags in the past that had a perforated space blanket inside, and were advertised as being very "warm" by having very low weight.
Total crap. Didn't work when they were new, and didn't work when they were used, exept the space foil had crumbeled to pieces soon and thus provided some quiet sleep.

So this leads me to the conclusion that a typical (down) bag blocks direct heat Radiation, and all that counts in the total heat transfer is convection and radiation off the outer surface of the bag (plus some evaporation).

All heat from the body travels through the bag and makes it's way to it's surroundings. (though there is a small storage ability). It's simple energy transfer, and is what the body put out will find it's way eventually into outer space.

And that's where the physics come in, it's you against outer space, which is apx 3 degrees above the lowest temperature possible (several hundreds of degrees below body temperature). As such radiation is very relevant and the main reason for tent condensation. It all depends on what is is between you and outerspace, air clouds? tree tops? tent, bag. And there is the earth below and the air at a temperature.

But it is possible on a clear night to form ice with a exposure to the night sky even though the temperatures are far above freezing and that method has been practiced by many primitive people (particularly in desert environments), so the temperature of space, and radiation, is very relevant.

So even though the surface of the sleeping bag does not feel 'body' warm, it is very warm compared to where the heat is going.

[Leo L.]

When doing some Google research, you come across tons of text for this topic (even some older WB threads).
Now it's always difficult whom to believe, when you read all this opposing opinions.
But some of the guys that sound really knowledgeable and serious, state two things:
- reflective (aluminiumized) coatings wear off too easy
- in real life conditions, any effect of heat radiation reflection could hardly been felt.

[Venchka]

Everything old is new again. Probably still doesn't work. Tent walls would be the last place to use this stuff for a variety of uses.
https://books.google.com/books?id=TO...xolite&f=false

I own a Texolite based sleeping bag liner. I don't use it inside a sleeping bag because I can't prove that it does anything. I don't use it alone because I can prove that it doesn't work.
There is no free lunch.

Wayne

[Dogwood]

So, Mekineer where are you an engineering or mathematics student? Let me guess NYU, Rensselaer, Syracuse? Takes one to no one. University of S. Florida and New Jersey Institute of Technology.

Some comments: The OP's pic is of a single wall emergency shelter. Think about the differences that can typically occur under emergency or survivalist situations compared to typical winter backpacking/camping.
When referring to a tent fly that references double wall shelters/tents not typically single wall shelters/tents. Stephenson Warmlite and Brooks Range tend to market to climbers and mountaineers. How do these activities and the needs of those engaging in such activities typically differentiate from your typical winter backpacking/camping and how you gear up? Ventilation and condensation were indeed considered in the design parameters of both the Stephensons 2person 2CR and Brooks Range A2 Rocket.

I've been amending my cold weather sleep systems for winter backpacking/camping being mainly a hardcore LD hiker during all 4 seasons, non hardest core mountaineer, and as one doing some low level climbing with a very cheap(about $5) very light sub 3 0z SOL mylar layered Emergency Blanket. https://www.rei.com/product/813512/s...FQ0DaQodl84Pog I'll put one under me layered with a CCF pad and UL inflatable pad pushing up my R value as I think needed for the conditions tweaking the CCF and inflatable pad I use. I may use one like this with a tarp in a lean to config only reflecting heat back in two directions. I have done as Joshua has done here: https://www.amazon.com/Grabber-Outdo...owViewpoints=1


This way I'm not locked into a tent with reflective inner surfaces which I find are for a niche use. Sleeping in an enclosed tent with metallic reflective surfaces has made me feel like I was on an indoor tanning bed needing protective eye googles or a blindfold to sleep.

[rocketsocks]

I got an old "Slumberjack" dome tent from the '80's that has an aluminized rain fly, it is my understanding it was to minimize condensation from freezing, it a true double wall tent 4 season complete w/half moon zippered opening in floor.

[Toolshed]

F'ing noisy.

[mekineer]

https://en.wikipedia.org/wiki/Therma..._heat_transfer

If I had a 35F night and a human having slept in a sleeping bag for a few hours, and a pyrometer, I could measure the surface temperature of the sleeping bag. Let's say, for kicks, the surface of the sleeping bag is 40F (277.6K). 2 meters squared of sleeping bag surface area. Epsilon = 1 to get top estimate.

2*(5.67*10^-8)*(277.6^4 - 274.8^4) = 27 Watts

Average male generates about 75 watts sleeping.

Anyone have a pyrometer?

[mekineer]

Venchka, I searched for reflective sleeping bag liner, and found this: http://www.columbia.com/omni-heat-sl...er-UU9891.html
Hey! It's breathable. How breathable, is it comfortable?

[nsherry61]

Venchka, I searched for reflective sleeping bag liner, and found this: http://www.columbia.com/omni-heat-sl...er-UU9891.html
Hey! It's breathable. How breathable, is it comfortable?

Columbia's Omni-heat is a bunch of little silver dots on the inside of the fabric, so it is plenty breathable if the fabric is, although, probably only about 50% efficient at reflecting IR. By contract, the SOL Escape Bivy is more like Tyvek (surprisingly breathable) and reflects with more like 90%+ efficiency. There is a new mini version of the Escape bivy they came out with last year that is more bag liner sized.

[Dogwood]

See what Thermodynamics I and II, Applied Heat Transfer Mechanical Engineering classes can do. Can't even enjoy a counting sheep and wishing upon a falling star session on the beach at Fire Island.

[gpburdelljr]

If it was practicable, don't you think some entrepreneur would have done it and sold it to the government? (Think $600 dollar hammer).