Emissivity of alumized Cuben, Silnylon
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jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Emissivity of alumized Cuben, Silnylon on 04/03/2014 09:54:06 MDT Print View

James Marco sent me a sample of aluminized silnylon

David Drake sent me a sample of alumized Cuben

The aluminized silnylon is gray, a little shiny, like the aluminized silnylon I got from Seattle Fabrics years ago that they have discontinued.

The alumized Cuben is shiny, just like aluminum foil. One side is shinier.

I rebuilt my insulation measuring instrument from http://www.backpackinglight.com/cgi-bin/backpackinglight/adams-torso-simulator.html except I re-made the guard ring so it better matches the measurement plate. Maybe I'll write something up about this in the future.

I have this thing about fulfilling commitments, so since they took the effort to send me the samples, I wanted to measure and publish the results.

First I measured some breathable nylon and some aluminum foil. I had some 2.5 oz Apex underneath. I measured the temperature difference between the measurement plate at the bottom of the insulation and the air:

breathable nylon - 36 F
aluminum foil - 46 F

so, with aluminum foil instead of non-IR-reflective nylon, there's a 10 F increase - my sleeping system would be 10 F warmer.

Next, I assumed emmisivity of 0.9 for the nylon and 0 for the aluminum foil. This is just an approximation. Really, the temperature difference is all I can claim from this, and even that is a tricky measurement.

I measured with the alumized Sil and Cuben and measured temperature difference. I then interpolated to determine emissivity:

aluminized silnylon - 42 F - 0.35 emissivity
aluminized Cuben - 40.5 F - 0.5 emissivity

This is really surprising to me, because the Cuben is so shiny, I assumed it would have low emissivity like aluminum foil.

This was just one measurement on one night. It was only about 20% clear and 80% cloudy. I'm going to re-measure if there's ever another clear night, measure a couple times to verify repeatability, measure both sides,... Maybe what appeared shiny to me is actually the mylar side, and the less shiny side actually has lower emissivity.

Stuart R
(Scunnered) - F

Locale: Scotland
Re: Emissivity of alumized Cuben, Silnylon on 04/03/2014 15:15:35 MDT Print View

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.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Emissivity of alumized Cuben, Silnylon on 04/03/2014 15:31:37 MDT Print View

That makes sense, thanks

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

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 04/03/2014 17:13:48 MDT Print View

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.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 04/03/2014 17:35:55 MDT Print View

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...

David Drake
(DavidDrake) - F - M

Locale: North Idaho
Re: Emissivity of alumized Cuben, Silnylon on 04/04/2014 13:38:06 MDT Print View

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.

Edited by DavidDrake on 04/04/2014 13:39:45 MDT.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Emissivity of alumized Cuben, Silnylon on 04/04/2014 14:46:37 MDT Print View

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.

David Drake
(DavidDrake) - F - M

Locale: North Idaho
Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 04/04/2014 16:21:52 MDT Print View

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.)

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 04/04/2014 16:57:02 MDT Print View

"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

Todd Taylor
(texasbb) - F

Locale: Pacific Northwest
Re: Re: Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 04/04/2014 20:29:27 MDT Print View

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).

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 04/04/2014 21:38:18 MDT Print View

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

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Emissivity of alumized Cuben, Silnylon on 04/18/2014 11:18:24 MDT Print View

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).

Adam Kilpatrick
(oysters) - MLife

Locale: South Australia
Re: Re: Emissivity of alumized Cuben, Silnylon on 07/27/2014 03:29:13 MDT Print View

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.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 07/27/2014 07:35:04 MDT Print View

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.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 07/27/2014 09:04:12 MDT Print View

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.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 08/20/2014 21:37:51 MDT Print View

Jerry,

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

Edited by richard295 on 08/21/2014 12:59:32 MDT.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Re: Re: Emissivity of alumized Cuben, Silnylon on 08/21/2014 00:43:54 MDT Print View

>"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.

Tyler N
(mantaray) - M

Locale: Vuur-Gin-Yaa!
Whaa? "Aluminized cuben" ? on 08/21/2014 14:46:16 MDT Print View

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.