Shiny foil inside your tent

[Gazmatron]

This year I’m determined to stay cool in my tent! I’ve just come up with an idea… Let’s see if it can stand up to ePlaya peer review!

I’ve been racking my brains the past few days trying to think of a cost-effective, Playa-proof way to use a highly reflective foil-type material to keep the sun’s energy out of my tent.

Silver tarps, aluminet, mylar, and various building insulation materials are often discussed…. As are the issues people have come across such as wind damage, and layers of dust causing the surface to lose its reflective properties.

Much of the discussion I’ve seen is around the use of reflective materials on the outside of structures/tents, but I’m interested to know if anyone has had success using any type of shiny shiny on the inside? In theory this should work well as it’s protected from the wind, and won’t lose its shine due to dust… and even if it does get dusty, you can reach it on the inside, so easy to wipe down.

When it comes to heat, I suspect many people are more familiar with the concept of reflectivity than emissivity, so I’ll explain... In non-scientific terms, emissivity is a measure of a materials ability to emit heat radiation. For example, brick has a high emissivity and aluminium foil has very low emissivity. Thus, if you hold your hand a few inches away from a hot brick you will feel the radiated heat, however if you wrapped that same brick in foil you would no longer feel the heat at the same distance.

So, in theory, if you attach a foil material to the inside of your tent (shiny side inwards), no matter how hot the outside gets, only a small percentage of that heat will be emitted (via radiation) inside your tent.

This is a bit counter-intuitive, so I’d be interested to know if anyone has tried it? As most reflective films and foils are very light, I figure you could fix it to your tent using a strong double-sided tape. Obviously, needs to be tape that can handle a bit of warmth, but I’m sure a bit of experimentation could yield a suitable product.

Can anyone suggest any reflective foil/film materials that aren’t too noisy when they move around (Mylar tends to rustle)? Also, any ideas for really strong double-sided tape?

[trilobyte]

So you're basically going to turn your tent into a large version of one of those foil-lined bags they use to keep pizzas and other food hot when they send them out for delivery. That doesn't sound like a really great plan, if your intent is to keep cool.

[Gazmatron]

So you're basically going to turn your tent into a large version of one of those foil-lined bags they use to keep pizzas and other food hot when they send them out for delivery. That doesn't sound like a really great plan, if your intent is to keep cool.

Hahahaha... yes, exactly. But don't laugh too much... I'm quietly confident the science is solid...

Joking aside, obviously it would also do a good job of keeping body heat in, so some air flow will be required... but that's easy enough to sort out

[trilobyte]

Of course the science is solid, those bags do a GREAT job of keeping the contents warm.

Seriously, your plan would likely do a far better job of trapping the heat inside than it would of reflecting the sun's energy away. In fact, it wouldn't really be reflecting any of the sun's energy away since the sun's rays would be hitting the tent and not the shiny foil material.

I say do it anyways. You'll probably survive (so long as nobody tries to sleep in it during the day), and probably come away with some really hilarious stories about the experience.

[Christian The Jew]

Put it on the outside to REFLECT infrared rays from the Sun, which cause your tent to heat up.

[theCryptofishist]

Put it on your head to keep your brain from heating up...

[theCryptofishist]

Of course the science is solid, those bags do a GREAT job of keeping the contents warm.

Those emergency mylar blankets work, too.

[ygmir]

I believe the science you are after, is the reflective coating reflect the emitted heat (emitted via infrared), which is solid. But, you want the shiny part facing out, with a minimal air gap. the infrared light, which transmits the heat energy, has to jump an air barrier (IIRC) and then be reflected. If they touch, the heat transfer can then be conductive, and foil is a great conductor, and will emit the heat from the other side.
That is the reason the foil and brick thing you discuss workds.......if the foil were applied perfectly flat, with full contact to the hot brick, your example would not work, or not nearly as well.
The issue then would probably be the heat trapped between the tent material, and the foil.
I's suggest some of the shiny, mylar bubble stuff, covering the outside of your tent. It tough, so you could brush it off if covered in dust, and much easier to install, etc.

this all, considering you are not able to just put a shade structure of some sort, over your tent, to keep direct sun off.

[lucky420]

i love baked potatoes

[Gazmatron]

Ha, I can see I’m gonna have a hard time explaining this one! Maybe I should start a science camp. We can have physics Tuesday, Chemistry Wednesday… and err, Biology Thursday…

Ygmir is on the right lines, but not quite… I do mean the reflective surface facing in… Think if it this way… Foil is just as efficient at NOT giving off heat as it is at reflecting heat. We’re not talking about reflection here – we’re talking about emissivity.

To use the aluminium foil example, the reason a hot brick wrapped tightly in foil doesn’t give off much heat is not that the foil reflects the heat in. The foil is in contact with the brick, so as a metal it conducts heat very well. However, because the surface of the foil has low emissivity, it doesn’t radiate heat outwards, away from the brick.

I’m not a physics expert, so probably not the best at explaining the principle… Anyway, I’m gonna build it and you can all come round and marvel at the next revolution in Playa shade design…. Unless I’m wrong, in which case better bring some bacon.

[maladroit]

You forgot convection. Your tent will be an oven.

[Gazmatron]

You forgot convection. Your tent will be an oven.

I'm expecting there to be a catch somewhere, but I think I'm still good for now... Convection requires a heat source, so I assume you mean heat conducted from the skin of the tent to the foil and thus into the air inside... Imagine the outside skin of the tent is the hot brick from my last example, there will be conductive transfer to the foil, but because of the low emissivity of the foil surface, there should still be very little radiated heat transfer into the air inside the tent. In theory, no more than would get through if the foil was on the outside acting as a reflector....

[Jackass]

Would u like a hat to go with that?

foil.jpg

[theCryptofishist]

You better bring some bacon as well. To some of these people, not having it will only turn into an unpleasent scene if they catch you in an overheated tent and their thoughts go to long pig.
after all, science without bacon is like bacon without science...

[Lonesomebri]

Why keep this to yourself? It has Theme Camp or Art Project written all over it.

[LowePro]

Ugh, do a test run for sure. I doubt it will work.
There will be an air gap between the tent material and the foil (no matter how tight you rig it, the wind and stretch will make this gap unavoidable). The air in this gap layer will heat up like crazy. The sun's rays passing thru the tent vinyl gets HOT, and the energy bouncing back off the foil layer will make the air layer ever hotter. This layer of very hot air will form a superheated "shell" of air around your inner foil "chamber". The hot shell of air will be way hotter than the ambient air temp and will cancel out any beneficial effect of the foil wrap. The foil isn't air tight (or else you'd.....die) so some air exchange from the superheated air into the foil chamber will occur.
Reflective surfaces work best as the outermost layer with an air gap below the foil and the next layer, that's Playa tested. Your proposal does the opposite.

"there should still be very little radiated heat transfer into the air inside the tent. " This might be true if is the foil was air tight, but it's not, a boy's gotta breath, right!

"In theory, no more than would get through if the foil was on the outside acting as a reflector...." Except you are creating layer of superheated air that will be WAY hotter than the ambient air temp.

A good way to test it would be to set your tent up in the hot sun, wrap yourself completely in a foil emergency blanket inside the tent and see how you feel. Or wrap an icecube in foil and put it into your car on a hot sunny day and see how quick it melts, compared to a foil-wrapped icecube outside of the car.

Alternatives: A mini monkey hut or shade rigged OVER your tent. Reflective or not, this is the tested way to a cooler tent.

[Captain Goddammit]

I think you are both arrogant and a fool.
Just because people are telling you there is something wrong with your plan doesn't mean they don't understand the science.
You seem stuck on one point about how emissive aluminum isn't, while overlooking convection and other factors.
I hope you build this little oven. You never learn as well as when you learn the hard way!

The Big Oops of your plan is that it doesn't matter how poorly your reflective surface emits heat. The heat would already be in your tent. The usual idea is to keep all that heat from reaching the tent in the first place.

[gaminwench]

OP first line
"Let's see if it can stand up to ePlaya peer review"

I think you have your answer(s).

[EspressoDude]

instead covering the inside of your tent, why not just wrap your body? a lot less foil needed.

[theCryptofishist]

The OP may have been named "most likely to cook in solar oven" in high school.

[Eric]

Ha, I can see I’m gonna have a hard time explaining this one! Maybe I should start a science camp. We can have physics Tuesday, Chemistry Wednesday… and err, Biology Thursday…

How about theoretical science vs. practical science day?
Your concept might seem valid based on theoretical science, but in reality you're going to turn your tent into more of an oven, not less. Any heat build up during the day will stay in there; any heat your body radiates at night will build up in there; the sun will still heat up the exterior of your tent the entire day without any mitigation, and that heat will cause the inside of the tent to get hotter (and your foil will help trap that heat); if you build air vents to allow air to circulate you're just allowing access to more dust - with no guarantee that it will let in enough airflow to cool the tent down. It's the airflow that is critical to a shade structure working, and you need lots of it - your design limits that to the point of non-existence.

I would spend the energy you're wasting on this plan to come up with a tried & true shade structure you can get to the playa from Reno. All you need is something that covers your tent & has a large air-gap between the inside of the shade and the outside of the tent. The more distance between the shade structure & the tent (within reason), the better the cooling.

[ACfromSAC]

See: Tent under Monkey Hut
or
HEXAYURT!

Last year was my first burn using the hexayurt and it is now nearly as essential an item as water and a bicycle. It kept my sleeping quarters dark in the moring, stayed remarkably cool AND blocked out quite a bit of noise as a bonus. I almost slept TOO well, it was hard to get moving in the morning. I highly recommend it. It's a breeze to assemble, relatively inexpensive and seriously will transform the comfort level of your week.

[BBadger]

Radiant barriers can reduce the amount of radiated heat you receive in the ideal case, but radiation is not really the main source of heating when you're in a tent under a shade structure. You're not camping in a vacuum. So even with using a shade cloth with perfect 1.0 emissivity, you're not going to feel 50% of the light's energy on one surface coming out the other side of the shade cloth.

You're probably thinking of radiant barriers on objects such as silvered styrofoam containers. The thing is, such barriers are fixed to insulation with high R-values to begin with. A high R-value impedes the effects of heat conduction and convection The silvered lining adds one last layer of protection from the outside world, from the perspective of the insulation, from affecting the insulation.

Here's you're sort of taking an opposite approach with foil on the interior. The heat is outside, you're on the inside. Sure, the foil reduces the emissivity of the surface, but there's not all that much radiation to begin with on the interior. The conducted heat would need to be converted back into radiation. Were you in a vacuum, the surface would absorb heat until it reached thermal equilibrium, and then radiate whatever it received back out -- but again, you're not in a vacuum.

The sun is bombarding the outside surface, which is often covered with dust and absorbs the sunlight relatively well. The surface of the shade cloth heats up due to the absorbed sunlight. While the foil may prevent light/infrared from radiating into your environment, it does nothing to prevent heat from conducting to the air adjacent the foil. Aluminum is, after all, a great conductor. You'll feel the heat of the air right next to the surface of the foil, and it's not because of thermal radiation.

The main contributor of heat will therefore not be radiation, but conduction/convection. This is why it is so important to have good airflow in a shade structure. It moves that hot air that gets conducted too the interior. It's easy to achieve good shade, but without airflow, the conducted heat has no place to go. After all, your own body produces heat and will heat the structure regardless of the heat of the sun.

The reason people use stuff like aluminet is because it reflects heat away, and also provides airflow. Black shade-cloth also works, but suffers because it both absorbs and emits sunlight easily, and provides little airflow when at adequate shade levels. Still, it provides shade and is usable given enough airflow. I prefer a silvered tarps because they're durable, opaque and reflective,. The only problem is that I need to ensure proper airflow because they're solid. A monkey hut has open ends, so this is generally not a problem.

Why would I not use foil? Because you might as well just use a silvered tarp and concentrate on the structure, not the surface material. Foil will also be fragile no matter where you put it, making it inappropriate for the playa.

[gaminwench]

and the meatcake has spoken.

next?

[Gazmatron]

I thought this might make for an amusing discussion… (and cop some abuse!) …Thanks for the helpful comments re shade structures etc. I do have a shade structure, but not everyone I know is able to build one – overseas logistics etc. mean some people just want to make the most out of a minimal amount of equipment...

I realise this is not going to be as effective as a shade structure over the tent. I’m specifically thinking about scenarios where for whatever reason a shade structure is not possible and the aim is to get the maximum amount of extra time in the tent in the morning, before it heats up and sleep is no longer possible. (Extra time being defined as anything over and above what the tent would provide by itself).

@Jackass, ha, damn right!

@asr9754 & BBadger, much appreciated – that got me thinking…. I genuinely want to understand the physics of this stuff better….). So picking up on some of those points:

If you used a single sided film, that would reduce reflection back into the air gap around the liner of the tent. We would still have a scenario where the surface of the tent and the air between the tent and the film would get pretty hot. However, would wind on the outside of the tent not also remove heat that is conducted either from the air gap or the surface of the tent, so to what extent it became super-heated is an interesting question…

Regarding inwards conduction, over a period of time, sure, the inside of the tent would become bacon-making hot. My thoughts are more about how long it would take for this to occur. I’m speculating that with the foil on the inside, the rate at which heat would be conducted to the air inside the tent would be much slower than if you didn’t have foil… Would the overall effect be so different to placing foil directly on the outside? Either way, a certain amount of conduction occurs and the tent heats up... Would the rate at which the tent heats up be significantly different either way?

Once the tent gets too hot to sleep in, I’m not worried about how much hotter it gets due to heat retention – this is about delaying that heat build-up. So I guess the question I’m trying to answer is whether such a contraption would give you a worthwhile amount of extra sleep… or would the effects of conduction and a super-hot outer layer negate the emissive qualities of the foil?

[LowePro]

Any marginal short term benefit that might occur by deflecting some of the early morning heat would be negated and more by the fact that the human body generates its own heat, and this heat would be trapped inside the foil chamber. You should test it out. Points for creativity, but I just don't think this would keep you cooler at all. There's a reason people use a foil emergency blanket to stay WARM rather than COOL.

There are some amazingly compact shade structures out there that will fit over a tent. And you can get creative mounting silver tarps off of pickup trucks and rebar stakes, so overseas travelers can still get some shade.

[Gazmatron]

Any marginal short term benefit that might occur by deflecting some of the early morning heat would be negated and more by the fact that the human body generates its own heat, and this heat would be trapped inside the foil chamber. You should test it out. Points for creativity, but I just don't think this would keep you cooler at all. There's a reason people use a foil emergency blanket to stay WARM rather than COOL.

There are some amazingly compact shade structures out there that will fit over a tent. And you can get creative mounting silver tarps off of pickup trucks and rebar stakes, so overseas travelers can still get some shade.

Fair comment, though I was thinking that body heat thing could be solved. For example, you could leave the door of the tent uncovered and have it on the west side. How much would need to be uncovered for sufficient body heat to escape I'm not so sure, but any uncovered tent should be quite efficient at releasing heat at night...?

[trilobyte]

You'll either have cracked it and will have done the one really glaringly obvious thing that nobody (including tens of thousands of overseas and long distance burners) has done successfully on the playa and posted on the internet in the last decade, or you'll discover firsthand that all those people with their common sense and years and years and years of experience on the playa were right. Go for it, at worst you pull the mylar out after the first campmate goes to ESD with heatstroke and spend the rest of the week in ez-bake ovens tents under the sun. Victory or hilarity, sounds like a win-win.

[Sham]

You may consider basting yourself with butter and some seasoning salt prior to going to sleep. I think you'll wake up a delicious golden brown.

[Simon of the Playa]

You may consider basting yourself with butter and some seasoning salt prior to going to sleep. I think you'll wake up a delicious golden brown.