May 25, 2010 at 12:33 pm #1259427
Having fallen in love with my Fugu Jacket which has an aluminum(?) reflecting layer of sorts forming the inside of the jacket, I was wondering why this isn't incorporated into more sleeping bags?
The idea is to mate an emergency blanket with a sleeping bag.. maybe just underneath the outer shell of the bag. Given that a reflective blanket weighs 2 oz, I'd think one cut to size in the bag would weigh 1 oz or less.. and would add a lot of warmth for an oz.. more than 1 oz of down would.
Anybody?May 25, 2010 at 12:44 pm #1613663
The reflective quality really does not do much. It does act like a vapor barrier, but that isn't going to do that much for you unless it is very cold.
I would go for the extra ounce or two of down.
–B.G.–May 25, 2010 at 12:48 pm #1613664
I assume this aluminum coating will breath?
I believe Mylar that space blankets are made from does not breath. the other night up on the PCT my friend went to sleep in his down bag with his non-breathable rain coat on thinking he would be warmer. He woke up in the middle of the night shivering and all wet. I did not have the hear to say "I told you so"May 25, 2010 at 12:49 pm #1613665
I get the vapor blocking but don't people lose heat through radiation much? I guess conduction to the ground is the primary mode of heat loss but thought perhaps radiation isn't too far off..
I think the radiation blocking was the reason the FUGU scored so abnormally high on Richard Nesley's chart measuring insulation of different down jackets.
PS: Not sure if the FUGU jacket's coating is breathable..May 25, 2010 at 12:57 pm #1613669
"I get the vapor blocking but don't people lose heat through radiation much? I guess conduction to the ground is the primary mode of heat loss but thought perhaps radiation isn't too far off.."
I did not state that there was no radiated heat loss. It just isn't that much as compared to conduction.
If you are standing upright, your body has some amount of radiated heat loss. But then in sleeping position, it is completely different.
–B.G.–May 25, 2010 at 1:15 pm #1613671
Yes, you lose a significant amount of heat via radiation.
A full radiant barrier wouldn't be breathable. Some companies have been playing around w/partial radiant stuff in clothes (shells from GoLite come to mind), but not sure how it would work in sleeping bags.
An emergency bag liner used as a VBL can easily add 15 degrees or more to a bag. You would need many more ounces of down to achieve the same result.
The VBL liner must be used as a liner, not as an overbag. If it were over, or used as part of the outer shell, then the insulation would get wet.
VBLs/radiant barriers can add significant warmth; I've used them regularly in temps as high as the 40s. I've only ever been warmer. They can't really make you colder if used properly. Most people would recommend that you don't use them above freezing.
Warmlite does use such technology in their sleeping bags, and has for decades. They aren't exactly seen as mainstream or as using mainstream philosophies, though.
Most people aren't comfortable w/VBL and find it harder to regulate their body temperature. I suspect that w/radiant barriers it could be difficult to manufacture an aluminized fabric with the same lifespan as a typical lightweight nylon.
Using a reflective blanket independently of the bag adds flexibility to your system. If you're cold, you can toss the 1.5oz liner in and add 15*F of warmth. If you're warm, don't bother.May 25, 2010 at 1:24 pm #1613679
"Yes, you lose a significant amount of heat via radiation."
The last measured data that I saw said that radiation was around 8% of total heat loss in a sleeping human. That varies from person to person. So, no, a 1.5 ounce reflective liner would not add 15 degrees F of warmth.
A vapor barrier can offer a lot of apparent warmth, but that gets into more variables.
–B.G.–May 25, 2010 at 1:46 pm #1613692
"So, no, a 1.5 ounce reflective liner would not add 15 degrees F of warmth."
Gotta agree with that. It will add a little extra warmth, but probably not as much as the same amount of extra down. Not only that, but I personally find liners to be a PITA. I get tangled and twisted in them something chronic! However, if you could add a reflective liner fabric such as used in the Fugu without adding any extra weight, it might be worth it.May 25, 2010 at 1:56 pm #1613695
@nerdboy52Locale: "Alas, poor Yogi.I knew him well."
I use my Heetsheets emergency bivy with by sleeping quilts all the time. I can get a good 15 extra degrees F. when I use it inside the bag. You won't get too moist if you keep the top of the quilt a bit open.
When I'm getting a lot of condensation or rain seeping or splashing into the tent, I use the Heetsheets on the outside of the bag. Let part of your body stick out of the quilt, and don't keep it too tight at the top. You'll get a bit of internal moisture, but not as much as you would have gotten from the rain. It's a great way of keeping your quilt or bag relatively dry.
StargazerMay 25, 2010 at 2:19 pm #1613709
@redleaderLocale: Luxury-Light Luke on the Llano Azul
The reflective coating has been used, on and off, for more than twenty years. It might give you some benefit when new but the reflective coating on my sleeping bag lost its "shine" after a half dozen uses.
It's all "flash" and no heat.May 25, 2010 at 2:34 pm #1613720
Seems we are talking about several things here. One is merely a reflective coating which reduces radiant heat loss and nothing more. This would not add terribly much warmth to a bag by itself. But some are also talking about VBL, which reduce heat loss due to evaporation of perspiration, and the airtight nature also reduces convection. A space blanket type liner would do all three. Stephenson's warmlite bags use a VBL but not a reflective coating, however they use a reflective silnylon on their tents to assist as a radiant barrier. Fugu uses a reflective fabric which is not a VBL.May 25, 2010 at 2:47 pm #1613724
@nerdboy52Locale: "Alas, poor Yogi.I knew him well."
>A space blanket type liner would do all three.
Exactly right. I'm suggesting a space-blanket type instead of a more permanent solution because you can use it situationally and in just the right way to achieve your specific goals.
Tain't perfect because you'll get some sweat buildup, but it beats the alternative — freezing your buns off or getting a very wet sleeping quilt/ bag.
StargazerMay 25, 2010 at 2:48 pm #1613725
@danepackerLocale: Mojave Desert
My old Caribou Mountaineering synthetic winter bag has a needle punched (for breathability) reflective mylar liner. I can't really say if it helps much, probably a little.
I don't notice any dampness with that bag so it breathes OK.May 25, 2010 at 2:59 pm #1613726
"I'm suggesting a space-blanket type instead of a more permanent solution because you can use it situationally and in just the right way to achieve your specific goals."
I'm guessing the OP wanted to know if a non-VBL reflective liner is available as part of a sleeping bag, and to my knowledge there isn't anything on the market at the moment, and the debate is to how much extra warmth would be gained from such a fabric. It's a legit question as many of us don't like using liners, though I do use a (non-reflective) VBL.May 25, 2010 at 2:59 pm #1613727
A rep told me that Columbia bags (remember, now associated w/ MH) is messing around with reflectives in sleeping bags. I can't remember if we talked about whether or not it was a VBL or not. I've been keeping my eye out for them as a curiosity. It'll probably be one of those, does- everything- sorta- well, but nothing superbly things.May 25, 2010 at 3:35 pm #1613746
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
Marketing spin. Gotta get an edge somehow.
Customers wouldn't know the difference anyhow.
CheersMay 25, 2010 at 3:56 pm #1613753
Since the OP specified "an emergency blanket," my suggestions did include VBL comments.
I don't recall exact statistics off the top of my head; my recollection from previous threads and medical texts was that our bodies lose ~60% of heat due to radiant heat loss. Clothing can stop some radiant loss, but not all. There was some good discussion here: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=31879 and in other threads.
It sounds like not everyone commenting has actually used a VBL. I have. It does work, and it does add about 15*F warmth for me. I hesitate to mention exact conditions or sack because of the propensity for hyper-analysis here, but I've slept in a VBL mylar bag alone in temps in the mid-40s or so, IIRC.
That's not hypothesis, that's fact. Just sayin'…May 25, 2010 at 4:29 pm #1613771
"Since the OP specified "an emergency blanket," my suggestions did include VBL comments."
Oh, it would help if I read the OP more thoroughly :(
Yes, a VBL reflective liner would add a good deal of warmth to a sleep system. This is why my cuben quilt is warmer than a pertex system of the same size and fill. Now, reflective 0.33oz/yd cuben fibre would be an awesome invention!!May 25, 2010 at 4:54 pm #1613778
"I don't recall exact statistics off the top of my head; my recollection from previous threads and medical texts was that our bodies lose ~60% of heat due to radiant heat loss. Clothing can stop some radiant loss, but not all."
Brad, you keep dragging in this irrelevant information. The OP asked about this in a sleeping bag. The implication there is that the person is horizontal on the ground. There, the radiated heat loss is something very low like I stated. It is completely different when the same person is standing upright, perhaps walking. There, the person is producing a lot more heat in general, and it has to go someplace. So, it leaves mostly by convection and goes out mostly around the shoulders, neck, and head.
Horizontal and vertical are two different situations.
–B.G.–May 25, 2010 at 5:18 pm #1613787
Conduction and convection (when it windy out) will suck more heat out you in your sleeping bag than Radiant heat loss. the emergency blanket helps with all three types of heat loss but is better with radiant than the other 2, depending on how tight you have it wrapped around you :)May 25, 2010 at 5:40 pm #1613801
Lynn, I think Colin Krusor posted something awhile back about aluminizing cuben. Lotsa $$$ though. Cubic Tech does produce an aluminized cuben, but the sample I have is much heavier than the .33…
Frank, thank you. Pretty much my point. You can stop heat loss two ways or three ways.May 25, 2010 at 10:40 pm #1613914
@kwilletsLocale: San Francisco
I was curious after reading about the Fugu here the other day, and some web searches turned up the following patent: http://www.freepatentsonline.com/6824819.html. It sounds like the fabric used in the jacket, but I haven't found any available. The patent holder is Milliken, http://milliken.com.
FIELD OF THE INVENTION
This invention relates to metallized fabrics which are durable to washing and wear. They can be used to down-proof articles in which they are used as linings, e.g., down and fiber filled, insulated articles of clothing and sleeping bags.May 26, 2010 at 12:57 am #1613940
@jephotoLocale: New Zealand
Almost 30 years ago now I had a Mountain Equipment synthetic bag with a silver radiant barrier in it. The concept didn't seem to catch on widely, but I did find this online http://www.livefortheoutdoors.com/Gear-Reviews/Search-Results/Sleeping-bags/Mountain-Equipment-Mithril-II-/. They claim it adds 3 degrees to the bag.May 26, 2010 at 6:06 am #1613964
Bob G., I would like to know what the conditions were for your quoted value. Until those are given, the number you presented and your resulting claims are irrelevent.
Richard Nisley estimated the IR barrier on the FUGU was equivalent to having ~2oz extra 800fp down (see his post on 01/10/10 16:18:39 MST):
I think this idea has merit. It is certainly easier and cheaper than ripping open a sleeping bag and adding some equivalent amount of down.May 26, 2010 at 7:25 am #1613984
I'm seeing a scary amount of conjecture and misinformation in this thread. Recommend everyone read this:
Radiation is a very significant heat loss mechanism which is why Aerogel jackets are so insanely warming because Aerogel is a near perfect IR barrier and thus prevents much heat loss from blackbody radiation.
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