View Full Version : Reflective Inner Tent Surfaces for Cold Weather
mekineer
10-03-2016, 20:50
How come tents don't come with radiation reflective surfaces on the inside of the tent?
For example, this emergency tent:
http://cdn3.volusion.com/moqgn.ooprv/v/vspfiles/photos/117-3.jpg
On a regular (non-emergency) tent, the inside of the rainfly could have a reflective surface, and also the flooring.
Tipi Walter
10-03-2016, 21:01
Durability, issue #1. Clammy wet condensation, issue #2. A tent must breathe, even single walls.
Slo-go'en
10-03-2016, 21:26
If you got a good enough sleeping bag, very little heat should be escaping which could be reflected back. And as Tipi said, condensation would also be a problem since what heat is escaping is your moisture laden breath.
mekineer
10-03-2016, 21:45
How much does a waterproof fly, breathe? I don't think much more than the air channels, and a full mesh inner tent.
Stephensons offer a reflective liner in their R series Warmlite tents specifically to reduce condensation.
You may need to search the net to see if it works or not.
Brooks Range had a version of their Rocket tent made with aluminumized (on the inside) Cuben Fiber.
Reports were that it was warmer than other single wall shelters but had a lot of condensation in spite of the 4 vents.
(the reflective bit peeled off after a while so it was discontinued)
colorado_rob
10-03-2016, 21:58
If you got a good enough sleeping bag, very little heat should be escaping which could be reflected back. And as Tipi said, condensation would also be a problem since what heat is escaping is your moisture laden breath.
I could be wrong, but I would think sleeping bags don't stop radiant heat. Only convective and conductive. Fabrics and goose down are probably transparent to IR, no?
If a durable, lightweight, breathable and reflective surface could be developed, why not. Tough order though.
Two more ounces of down in your bag, further reducing convection and conduction would probably do more.
mekineer
10-03-2016, 22:48
Looking around, I found these positive experiences with a reflective blanket: https://www.amazon.com/Grabber-Outdoor-127008-Weather-Blanket/product-reviews/B000CSJWWW/ref=dpx_acr_txt?showViewpoints=1
Also, some atmosphere thermodynamics can shed a little light: https://misfitsarchitecture.com/2013/03/01/its-not-rocket-science-5-night-sky-radiant-cooling
Speaking of thermodynamics: condensation happens because the air outside the tent is colder than the air inside the tent. The temperature at the tent wall surface creates a zone for water to condense. In other words, the "relative humidity" right at the inner surface of the tent wall becomes 100%. Granted, the breathing and sweating will add to the water vapor in the tent, but can be reduced a lot with a well ventilated tent. A non-breathable ground cover can also help reduce moisture in the tent.
2 more oz of down could be good too, but an overall warmer tent? For those of you that want a ground cover, couldn't you use a reflective one?
I guess to save weight, all the concentration on keeping warm should happen as close as possible to the human. So, the reflective surface should be part of (or inside of) the sleeping pad (and not a space blanket, because the body needs to breathe). But if you are going to let the body breathe, and you want reflectivity from all sides, I think the insides of the tent should be reflective.
I don't feel like getting out textbooks and trying to calculate what percentage of heat is lost from radiation, from a 35 degree night. Hasn't someone already done this? If the radiation loss is a substantial percentage, then you could also take out 2 oz of down from your sleeping bag, and be able to use a less bulky sleeping pad.
VBL's work by keeping your body sweat from cooling you off and keeping your insulation dry. Now if you have a reflective surface on the tent, water is going to condense on it and drip all over your insulation. Kind of defeats the purpose, don't you think? You still have to breath. Your moist air is going to condense on the cold surface of the reflective layer. Think of a mirror in a steamy bathroom.
mekineer
10-03-2016, 23:13
Egilbe, I think my post, 14 seconds before yours, answers that question.
colorado_rob
10-03-2016, 23:38
I don't think you guys understand radiant heat. We're not talking about making the tent any warmer, so not sure why condensation keeps being discussed, except if the actual reflective coating restricts breathing.
We're talking about the person in the bag feeling warmer, because some of his own radiant heat will be reflected back to him, making him feel warmer. Without the reflective coating, his radiant heat just goes out to space.
Matter of fact, a reflective coating could actually keep the tent surface cooler with less condensation, because it would absorb less heat.
It comes down to how big a percentage of his total loss is radiant, as mentioned below. I suspect it's small compared to other losses, I also suspect any practical coating a wouldn't reflect much back.
Or, I'm full of it because it's way late at night.
mekineer
10-03-2016, 23:42
Also, Franco wrote: "Stephensons offer a reflective liner in their R series Warmlite tents specifically to reduce condensation.", which is true, because if it is warmer inside the tent, there is also a lower "relative humidity" inside the tent. This is because a higher temperature allows more water vapor molecules to live inside the tent... which, can flow out of the tent, due to the fine tent ventilation, and then condense outside somewhere, when the air that was in the tent cools down.
Franco wrote: "Reports were that it was warmer than other single wall shelters but had a lot of condensation in spite of the 4 vents." Apparently, due to poor design, 4 vents was not adequate ventilation.
I was camping on the beach, on Fire Island 2 weekends ago, and was pleasantly surprised how much warmer it felt, once inside my tent... despite my tent having awesome ventilation. I ended up using my summer down bag as a quilt, dressed in base layers with no ground pad at all. The sand was a little cool, and I started thinking about some reflectivity to the top of the ground cloth, to make the tent even warmer.
I was browsing the web, and came upon someone that wrote about radiation coming from a sleeping bag: " As for heat radiating from the outside of a sleeping bag, the same amount radiates from a summer bag as a polar bag; otherwise the polar bag would retain over time until it was hot enough to bake you. The difference between bags is a high R factor means it takes longer for heat to radiate through to the outside of a polar bag. But once both bags have “warmed up” they will radiate heat with equal speed. " So colorado_rob is correct that, at steady state (http://en.wikipedia.org/wiki/Steady_state), sleeping bags don't stop radiant heat.
The radiant heat going off an idling, upright standing human body is usually more (about two times) than the amount of heat lost by convection and sweating.
So the radiant heat definitely is a considerable amount - in specific circumstances.
The radiant heat is calculated by a formula that contains the temperature ^4 - a very important figure.
Its emitted by a wide variety of wavelengths, infrared just being one of the more important ones.
There are materials that are transparent to infrared (PE foil being one, like (sil)nylon would be).
I'm not sure if the down filling would block infrared, guess it would by a certain degree.
If a sleeping bag would be completely transparent to radiant heat it would greatly help to throw a space blanket over a summer bag and feel comfortable in deep winter - which isn't the fact, so I guess the bag as a whole is not transparant to infrared.
Now the formula for the radiant heat comes into play, remember the temp is there T^4. So assuming all radiant heat is emitted off the outer surface of the bag, its important to know the temp of this outer surface. If using a good warm bag, this outer temp might be close to the air temp. So finally the radiant heat emitted through the bag doesn't seem to be too much. (I guess most of the heat losses while sleeping goes through contact to the pad, convection to the air and evaporation - a smaller part only through radiation).
Now the lower the temp of the emitting surface, the by far lower the radiation (remember T^4).
This leads me to the conclusion that a reflective coating of the innser side of the rainfly would help a little, but not as much as you would expect.
My old Salewa Sierre Leone had something like this, kind of a silver painting of the inner side. I never felt any difference whether I put the reflective side inside or outside.
(BTW, this coating was of poor quality and lost its reflectivity within short time).
The only time I clearly felt a difference was during a hot day in the desert we had to stay in the tent due to being ill, we put the reflective side outside, thus blocking part of the sun radiant heat away.
Remember the formula: T^4 - in really hot sun, it does make a difference.
illabelle
10-04-2016, 05:18
Interesting that you brought this up. I recently bought this tent for use with a kid's scout-type club. It's cheap, not lightweight, but serviceable, and I hope it's durable. The fly has a reflective layer:
The Bushnell Shield Series offers Heat Shield technology featuring a special reflective coating on the underside of the rainfly which blocks the sun's UV rays keeping the tent darker and noticeably cooler.
https://www.walmart.com/ip/Bushnell-Shield-Series-4-Person-Dome-Tent/41737128
mekineer
10-04-2016, 07:37
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 (https://en.wikipedia.org/wiki/Radiation_properties#Properties).
mekineer
10-04-2016, 07:40
illabelle, I think that tent is reflecting radiation from the outside, which is the opposite of what I was trying to achieve, which is to make the tent warmer.
mekineer
10-04-2016, 07:48
Leo, you wrote: "My old Salewa Sierre Leone had something like this, kind of a silver painting of the inner side. I never felt any difference whether I put the reflective side inside or outside."
I bet you would have felt the difference, close to a camp fire!
http://sectionhiker.com/brooks-range-mountaineering-ultralight-tent/
mekineer
10-04-2016, 08:04
I still feel confused. Those equations are for very simple situations. You have a complex system with many layers, that may require the use of integration (https://en.wikipedia.org/wiki/Integral)? Does the equation work for any two surfaces, regardless of what is in between them (maybe the equation requires a vacuum between the two surfaces)? Ok, never mind, I get the temperature at the sleeping bag surface, and simplifying to the temperature outside the tent. I guess the temperature of the sleeping bag could be measured, using a pyrometer. Wow, cool.
Pringles
10-04-2016, 08:09
I remember a Canadian brand tent, that I saw in a store maybe 15 years ago, that had a fly that was reflective. It wasn't a bright shiny reflective, but it was reflective. That fly could be used with the shiny side out, to reflect heat away, or you could flip the fly over and have the shiny side toward you, to reflect the heat back. I hadn't thought about it since I saw it, until this post.
garlic08
10-04-2016, 08:11
As Tipi said in post #2, durability. I once picked up a Z-rest pad with a mylar layer added, because it was the only one on the shelf and on sale, and the mylar layer was rubbed off after a few weeks of use. I have an emergency bivy with a reflective layer, used a few times as a reviewer, and it worked great--a few times. I deployed a mylar "space blanket" once back in the 80s in a borderline survival situation and it saved the day, but then was trash.
If a durable reflective fabric ever becomes available (and affordable) for tent use, I'd love to try it.
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 (https://en.wikipedia.org/wiki/Radiation_properties#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
10-04-2016, 12:49
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
10-04-2016, 13:30
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
10-04-2016, 15:12
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.
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.
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=TOADAAAAMBAJ&pg=PA77&lpg=PA77&dq=texolite&source=bl&ots=A4O96HNNEf&sig=68UogFJUpawPr1l9Jr19QqnonJc&hl=en&sa=X&ved=0ahUKEwiBucW7gcLPAhWFbSYKHTmNA5kQ6AEILzAD#v=on epage&q=texolite&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
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/sol-emergency-blanket?CAWELAID=120217890000862485&CAGPSPN=pla&CAAGID=15877490680&CATCI=aud-77557513944:pla-126979075960&cm_mmc=PLA_Google%7C404_11706%7C8135120001%7Cnone% 7C84cd9ac6-9390-4df4-84a2-df3fd6654ed3%7Caud-77557513944:pla-126979075960&lsft=cm_mmc:PLA_Google_LIA%7C404_11706%7C813512000 1%7Cnone%7C84cd9ac6-9390-4df4-84a2-df3fd6654ed3%7Caud-77557513944:pla-126979075960&gclid=CPaQtpuWws8CFQ0DaQodl84Pog 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-Outdoor-127008-Weather-Blanket/product-reviews/B000CSJWWW/ref=dpx_acr_txt?showViewpoints=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
10-04-2016, 19:11
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
10-04-2016, 21:24
F'ing noisy.
mekineer
10-05-2016, 18:39
https://en.wikipedia.org/wiki/Thermal_radiation#Radiative_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
10-05-2016, 18:56
Venchka, I searched for reflective sleeping bag liner, and found this: http://www.columbia.com/omni-heat-sleeping-bag-liner-UU9891.html
Hey! It's breathable. How breathable, is it comfortable?
nsherry61
10-05-2016, 22:03
Venchka, I searched for reflective sleeping bag liner, and found this: http://www.columbia.com/omni-heat-sleeping-bag-liner-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.
See what Thermodynamics I and II, Applied Heat Transfer Mechanical Engineering classes can do. :p Can't even enjoy a counting sheep and wishing upon a falling star session on the beach at Fire Island. ;)
gpburdelljr
10-06-2016, 10:31
If it was practicable, don't you think some entrepreneur would have done it and sold it to the government? (Think $600 dollar hammer).