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Emissivity of alumized Cuben, Silnylon


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  • #1315216
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    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.

    #2089315
    Stuart R
    BPL Member

    @scunnered

    Locale: Scotland

    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.

    #2089324
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    That makes sense, thanks

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

    #2089358
    James Marco
    BPL Member

    @jamesdmarco

    Locale: Finger Lakes

    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.

    #2089364
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    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…

    #2089658
    David Drake
    BPL Member

    @daviddrake

    Locale: North Idaho

    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.

    #2089676
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    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.

    #2089713
    David Drake
    BPL Member

    @daviddrake

    Locale: North Idaho

    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.)

    #2089726
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    "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

    #2089799
    Todd T
    BPL Member

    @texasbb

    Locale: Pacific Northwest

    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).

    #2089827
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

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

    #2094318
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    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).

    #2122673
    Adam Kilpatrick
    BPL Member

    @oysters

    Locale: South Australia

    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.

    #2122685
    James Marco
    BPL Member

    @jamesdmarco

    Locale: Finger Lakes

    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.

    #2122694
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    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.

    #2129045
    Richard Nisley
    BPL Member

    @richard295

    Locale: San Francisco Bay Area

    Jerry,

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

    #2129085
    David Thomas
    BPL Member

    @davidinkenai

    Locale: North Woods. Far North.

    >"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.

    #2129260
    Tyler N
    Member

    @mantaray

    Locale: Vuur-Gin-Yaa!

    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.

    #2145187
     
    BPL Member

    @rememberthelorax

    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.

    #2145194
    Justin Baker
    BPL Member

    @justin_baker

    Locale: Santa Rosa, CA

    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?

    #2145195
    Nick Gatel
    BPL Member

    @ngatel

    Locale: Southern California

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

    #2145204
    D M
    BPL Member

    @farwalker

    Locale: What, ME worry?

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

    #2145205
    Nick Gatel
    BPL Member

    @ngatel

    Locale: Southern California

    "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.

    Tyvek Tarp

    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.

    sun tarp

    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.

    PUG

    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.

    #2145217
     
    BPL Member

    @rememberthelorax

    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!)

    #2145497
    Tyler N
    Member

    @mantaray

    Locale: Vuur-Gin-Yaa!

    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!

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