Emissivity of alumized Cuben, Silnylon

Aluminized cuben is shiny because the mylar is transparent at visible and near-infrared wavelengths. This will make aluminized cuben good at reflecting heat during the day as the sun is hot and so most of it's heat is in the near-infrared.

However, mylar is NOT transparent at long-infrared wavelengths. The emissivity of mylar is around 0.4 at 10um. This means aluminium in a mylar sandwich is not so good at reflecting heat from low temperature objects, like body heat. How effective will depend on the thickness of the mylar. Aluminized mylar "space blankets" are probably fairly reflective, but cuben is made with much thicker mylar.

That makes sense, thanks

Someone said aluminum was on one side. Next time there's a clear night I'll measure the other side.

Thanks for the test, Jerry.
Yes, the space blankets are one sided. I am guessing they fold it before it enters the vacuum chamber. I have an old one around that is bretty well beat. Much of the aluminum is worn/corroded off. If I handle one side, it makes my hands black. Handling the other side does not. I can see the coating is almost gone in spots, because I can see through it, though not fully.

That was Cuben, not space blanket. Space blanket is just Mylar. I have some space blanket like that – kind of deteriorating. I've carried it around forever…

Thanks for doing this, Jerry.

I pulled apart a bit of aluminized cuben last night–it looks like it's made with a very thin ply of mylar, then the fibers (Dyneema, Spectra?), then a top ply of aluminized mylar. The aluminized mylar ply is thicker than the other mylar ply, and the fibers don't seem to adhere well to it. The dull side is definitely the thin mylar/fiber ply side.

Can't tell if the aluminum side of the aluminized mylar ply faces out or in–facing out might help with adhesion, but would expose the aluminum to more abrasion.

I doubt I'll make a tarp out of this stuff–too many problems reported with delaminating. Maybe bivy bottom. Maybe VBL bag liner (although I haven't really been doing trips where VBL would be a benefit.). Not sure if low emissivity would make a difference in those applications.

I have a bivy bottom of Seattle Fabrics aluminized sil. Couldn't tell if it made any difference.

My theory, which I haven't convinced everyone else of, is that you need an air layer next to the aluminum or it won't work. If you're touching the aluminum, it will conduct heat to make you the same temperature, so the fact that it isn't radiating doesn't matter.

So bivy bottom doesn't matter very much. Except where you're not touching it next to your body, there will be an air layer, so it would help there.

Wouldn't having a pad between the bivy bottom and you do give an air layer?

(Disclosure: never used a bivy–not sure I will in the near future. Except that I'm not fond of the bugs (and occasional other critters) using just a tarp in some conditions, so might make one in the future.)

"Wouldn't having a pad between the bivy bottom and you do give an air layer?"

No, because the outer surface of the pad will absorb IR

It has to be an air layer

But, it does get complicated and non intuitive

A "space blanket" is good – air space outside the space blanket

An aluminized sheet suspended between floor joists or studs is good because there's an air space on one or both sides

jerry wrote: "It has to be an air layer"

Actually, a vacuum would also work. :-)

This topic dominated one of the longest threads I've ever followed on another site. I agree with jerry–it's pretty straightforward physics. There's a net radiant heat exchange between two surfaces only if they are at different temperatures and can "see" each other. That heat exchange can be lessened if one or both surfaces has a low emissivity (high reflectivity). If they're touching each other, conduction short circuits things and the two surfaces end up at about the same temperature.

So to get the so called insulating effect of a highly reflective surface, it needs to be facing, but not touching, the other surface. That lets the two surfaces remain at different temperatures, which is what you want (i.e., you warm, other surface cold).

vacuum is good – it's called a thermos – a little heavy though : )

I measured again on a clear night. I had a layer of fleece with on top of it – foil, aluminized sil, aluminized Cuben, or eVent.

I assume the foil has an emissivity of zero and the eVent is 0.9. The eVent should remove the effect of adding another layer of material that adds a bit of an air layer. Also blocks any convection out of the fleece.

Data – temperature difference between bottom of fleece and the air temperature. I am putting out about 50 watts / square meter which is like the human body:
foil – 34 F, 0 emissivity
silnylon – 23 F, 0.5
Cuben – 19 F, 0.65
eVent – 13 F, 0.9

I assumed emissivity is proportional to temperature difference. This may not be valid but it should be close.

So if you compare eVent and foil, there is a 21 F temperature difference. If you put a radiant barrier on the outside of your sleeping bag, it will reduce the minimum temperature you're comfortable at by 21 F.

I measured both sides of the Cuben and it was the same.

I think most any normal fabric would be the same as the eVent.

The silnylon doesn't look real reflective, more of a gray. The temperature difference/emissivity is about half way between eVent and foil. Since radiative heat loss is a fairly small effect, you want the emissivity close to zero. I wouldn't bother using the aluminized silnylon.

The Cuben looks very reflective, just like the foil, but the data says the temperature difference/emissivity isn't much different than the eVent. Using the aluminized Cuben as a radiant barrier is not very effective. I measured this several times and kept getting the same result.

Space blankets are very close to zero, although I didn't have time to measure. If you want to prevent radiant heat loss, put a space blanket outside your sleeping bag (or clothes).

This is fascinating Jerry!

What are the weights of the reflective cuben, silnylon and foil?

21F difference for adding foil is quite significant. In a vapor barrier sleeping system it could be quite effective as an outer layer to a quilt.

I wonder how hard it would be to glue/laminate space blanket to .33 cuben fiber for strength. Probably painstaking.

There are a lot of assumptions here that may not pan out in the real world. Jerry is measuring *only* emisivity of the four materials. There are other factors that effect how comfortable you will be.
1) Conduction
2) Convection (a special form of conduction that includes circulation)
3) Humidity/air pressure which will effect density slightly.
Vapour barriers, et al, are typical with plastics, mylar and cuban. Both eVent and SilNylon will bleed moisture. (Fill a bag made of these with water and set them on a piece of paper…silnylon "dry" bags don't work that well.)

Then the more practical matter of bonding the correct side. Typically, space blankets are only aluminuzed on one side. So, you have a layer that may not adhere well or you have a layer that wears quickly. Not something you would want on a sleeping bag or tent designed for 5-10 years of use. Guy lines, loops, etc will provide avenues for condictive heat losses. Convection, winds, et al will provide avenues for convective heat losses. And you would need to perforate the space blanket to provide relief from himidity and condensation. I expect no more that 3-5 degrees F for a bonded sheet. Not the 21 that Jerry's numbers are showing. His numbers are accurate for testing, but not in use. I wouldn't rely on a space blanket if the temps were much below about 60F.

Aluminized Cuben is 1.2 oz/yd2 – I don't know if there are different weights availabile

Reflective silnylon is 1.8 oz/yd2

foil is 1.1 oz/yd2 but was just for testing – I assume it has emissivity close to zero – no practical value for camping

space blanket is 0.6 oz/yd2 (alumized mylar)

Like I said, testing is tricky so I wouldn't assume any of this is absolutely valid, more of an invitation for others to experiment. James had some good points about how this is complicated. I do measure outside in conditions that aren't that much different from when I go camping. I only measure at sea level, but I think that's a minor effect. I don't measure humidity but the humidity is typical of reality, so it's an uncontrolled variable – I think minor.

A major effect is wind. This was tested in still air. I think if it's breezy, you lose most of the advantage. I've been fooling around with this but need to wait for it to get cold again.

Richard tested emissivity with an emissivity measuring instrument. He measured that foil was 0.41, aluminzied Cuben was 0.51, space blanket 0.54. I think he got a different result originally but recalibrated his instrument. I got a much bigger difference with foil, but used a totally different measurement technique, but this shows that there are more questions than answers about all this.

If 21F was accurate, you would need about 1 oz/yd2 of down to give you that much increase in warmth. I think that is a better way to lower your comfort limit.

I think a space blanket as emergency warmth would be effective for the weight. You won't be warm but it may keep you alive. I see they use these in first aid or for runners at races to warm them up.

And when I have been out in the wilderness, I have measured 30 F difference between a meadow and under trees, on a very clear and still night, so that is a way to avoid radiative heat loss that I have confidence in.

If you do any emeperimenting and have useful results, report back.

Jerry,

I built a new emissivity apparatus and retested the samples. The updated results are posted Here.

>"And when I have been out in the wilderness, I have measured 30 F difference between a meadow and under trees, on a very clear and still night, so that is a way to avoid radiative heat loss that I have confidence in."

+1

And while you might not be able to quantify it without a thermometer, you certainly can feel the delta of a few degrees from one setting to another. Move out of the wind, under a tree, upslope a bit and note how much warmer you feel. Within 50 yards, you could often find a spot that 5-10-15 or more F warmer between the dry-bulb, windchill, and radiant effects.

Howdy folks – apologies for interrupting, but this thread caught my eye.
Is anyone currently producing/successfully experimenting w/aluminized cuben? The prospects are exciting. Sounds like a false start w/the Brooks Range Rocket a few years but maybe the material's integrity has been optimized. I tried to search BPL + Google but no luck – nada. Or is this only in the MYOG realm at this point?
I've been holding out on a proper UL 3-season shelter and this concept is making me (happily) hit the brakes if we may see this material at some point soon. Most of my adventures are in the SE so the sunblocking properties would be most welcome.

mantaray: Is anyone currently producing/successfully experimenting w/aluminized cuben?

Just wanted to drop-in really quick and let you know that I will be testing out an aluminized cuben fiber shelter next month throughout Death Valley and the Mojave Desert.

Photos and what limited information I have to share can be found here.

Scroll through the comments to read additional information and additional photos.

My thanks to Nathan Meyerson for sending me a very small sample of some of his fabric for initial testing. Thanks also to Joe from zpacks who secured enough from CTC to make the shelter for me for this unique hiking trip I am taking.

Sometime early to mid 2015 I will have a full white paper on this fabric, as I typically have done for new/prototype fabrics from CTC, and will provide it to anybody in the industry that wants it.

Thanks to everybody here at BPL that has been doing all kinds of testing and research on this fabric, it has helped me make the hard decision of choosing this fabric over other fabric I have been testing. Getting it out onto the trail is the next needed step to know whether we should push CTC to produce more. Over the next 90 days I hope to be able to put it through both hot and sub-freezing weather conditions. Will report back as I have gained insight into the fabric in real world, on the trail, use.

John, a month long trek sounds like a bad time to give this a first test run.

I've heard about those aluminized shelters delaminating badly.

Seems like it would be blindingly shiny in the sun.

Where are you going where it's 100 degrees in November?

It sounds like the aluminum is sandwiched between other layers, so lamination may not be a problem.

Awesome John, good luck with the experiment. Can't wait to hear about how it works out.

"Just wanted to drop-in really quick and let you know that I will be testing out an aluminized cuben fiber shelter next month throughout Death Valley and the Mojave Desert."

I spend considerable time every year in November and December hiking in deserts around Death Valley, Lake Mead, Joshua Tree, and the Mojave Preserve. The absolute last thing I worry about is heat. Sub-freezing temperatures at night? Yes, very common. By mid-November there are very few days in any of the areas near 80F, unless you are camped out in Badwater.

I have experimented with aluminized Tyvek tarps. Yes, they are a little cooler than a solid color nylon tarp; but the key factor during the day is airflow and pitching a tarp up really high with lots of ventilation. I wouldn't use something like a Hexamid design (my go to shelter) for sun shade — you can't get it high enough off the ground for good airflow. Of course I only use tarps for daytime desert shade in the summer where temps can exceed 120F.

Below is a Aluminized Tyvek tarp I played around with a few years ago.

Although I didn't do testing with a thermometer, but rather how I felt, it wasn't significantly cooler than the dark nylon tarp below, even when I pitched both exactly the same.

Delamination is a big problem with aluminized materials. I used many different kinds on my tent trailers for over 10 years. These were placed over the tent material of the camper, so the use was much milder than what a backpacker would put them through. These would last about 100 camping days before I had to replace them due to delamination, which was once a year. They did help keep the camper a little cooler in the summer, but we camp in the desert where few people go that time of year. BTW, I did some testing in winter by flipping the aluminum side down — didn't keep the inside any warmer than no cover.

Below is the tent end of my camper with an aluminized tarp over it on a September camping trip with ambient temps over 100F.

It sounds like the material you are testing has the aluminum sandwiched between two layers of material, so it may hold up better, or maybe not. For me to even consider a shelter like this, someone would have to thru hike the PCT or CDT and set it up every single night with no problems at all. Plus, I wonder how more effective it would be compared to a dark nylon tarp, which would probably cost 1/10th and last much longer.

But what do I know? I'm not a gear tester or scientist, just an old guy who gets to hike fairly often. Don't mean to sound snarky, if this comes across that way. But it seems we spend way too much time here on BPL talking about new gear when the stuff we already have works just fine.

Good luck on your trip and stay warm :)

I'll let the rest of you hash this out and. I'm heading up to Joshua Tree to cool off.

just to nip this issue in the butt before all of you have a hernia over it… (giggle – say that with a grin on my face)

I do not expect to have 100°f temps on this trip, but the reality is, it *is* the desert and *anything* can happen. I spent a good part of my life in the desert, I know as well as you guys do just hot crazy the weather there can be.

But allow me to explain.

I do not expect the thermometer to hit 100… you guys are mis-understanding me… or perhaps I did not properly clarify myself… or both :-D

I believe the terms here are "ambient temperatures" and "heat index temperatures"…

This year I have been down to DV/MJ a few times during the summer and I recorded the thermometer for three of the trips… 86, 92, 102. This was outside temps. A couple years ago I was in DV when it hit 116° in the shade. All of my trips were to do testing of fabrics I was working with different companies to R&D sun reflective fabrics and each time I setup different shelters. Within 30 minutes of setting up the shelters, I recorded the temps *inside* of the shelter. They were 98, 109, 126.

So, the point here is that I am not talking about having 100°f temp days due to how hot the heat index is, but rather how bloody hot it gets *inside* of the shelters. If you take/took the time to read my post and comments over at FB you will/would have read that I am planning on sleeping midday and hiking at night/mornings. So, I do not want to be using a shelter that is going to cook me to death… and sleeping under/in a shelter that is 100° is just about impossible, at least for me. So, yeah, its flipping November… and while I am not expecting snow or 100-degree temps, to expect there to be 80-90° temps (as well as the possibility of snow) during my hike is something I do have to plan for. And, if it is that hot, inside/under a shelter means it is going to be even hotter. Well, hopefully not… hopefully this fabric will actually make it cooler… that is the hope… hope… hope.

Sidenote: I specifically planned to be out on the trail at a very strategic few weeks of the year in november for optimal weather… october can still have high heat index, and late november and december can be… well, hella cold nights… I don't want to be freezing at night/morning when I am hiking.

Anyway, thanks for the well-wishes folks – it means a lot. Going to be the most challenging hike I have ever taken on. It will be a fun test for both myself and a few new pieces of gear that hopefully will be on the market in 2015 if all goes well on my hike.

Again, thanks everybody. Have a wonderful holiday season! (ps: keep the guys that are doing the pct winter hike on your mind, now that is going to be a serious challenge… they could use some good thoughts going their way!)

Wow John – what a mission. Sounds like you're heading into this challenge w/a good gameplan and (hopefully!!) great tech to persevere. Tackling this in the Mojave is even more dramatic. I wish you the best and look forward to updates!