Reflective Inner Tent Surfaces for Cold Weather

[mekineer]

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...otos/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]

Durability, issue #1. Clammy wet condensation, issue #2. A tent must breathe, even single walls.

[Slo-go'en]

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]

How much does a waterproof fly, breathe? I don't think much more than the air channels, and a full mesh inner tent.

[Franco]

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]

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]

Looking around, I found these positive experiences with a reflective blanket: https://www.amazon.com/Grabber-Outdo...owViewpoints=1

Also, some atmosphere thermodynamics can shed a little light: https://misfitsarchitecture.com/2013...adiant-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.

[egilbe]

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]

Egilbe, I think my post, 14 seconds before yours, answers that question.

[colorado_rob]

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]

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, sleeping bags don't stop radiant heat.

[Leo L.]

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]

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-...-Tent/41737128

[mekineer]

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]

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]

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!

[Cheyou]

http://sectionhiker.com/brooks-range...tralight-tent/

[mekineer]

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? 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]

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]

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.