Apr 25, 2010 at 9:55 am #1258138
I see alot of posts here claiming the reflective properties of a space blanket are insignificant, and that they are only good for preventing convective/evaporative heat loss. Yet the Neoair seems to rely heavily on reflection for it's R-value and there seem to be alot of folks who vouch for it's warmth, even though it has no insulation. So what's the verdict? does reflection work with the low heat output of the human body? would using a space blanket on top of a foam pad increase the warmth at all?Apr 25, 2010 at 10:02 am #1601821
Jeff PatrickBPL Member
For the space blanket to work, it can't be touching you. It needs a little airspace so the heat reflects instead of going through.
At Hennessey Hammocks they use a heat sheet as part of a pad system to keep the hammock warm and they have a video explaining this.
I imagine the neoair works by allowing your body heat in through the first layer and then reflecting it from the bottom layer back off the top layer and so on.Apr 25, 2010 at 10:16 am #1601827
Rick DreherBPL Member
@halfturboLocale: Northernish California
I suspect most of the NeoAir's insulative value comes from the inner baffling with some small added benefit from IR reflection.
RickApr 25, 2010 at 10:52 am #1601836
I have done a fair amount of winter mountaineering and I can attest that a mylar space blanket DOES help when used as a ground sheet. Definitely helps keep me a little more warm. Just IR reflection.Apr 25, 2010 at 2:25 pm #1601901
The only R-value from the NeoAir is the space blanket inside. The baffles are just randomized poly scrim, if you will… looks kinda like a fabric version of OSB board. Really just to hold the pad together.
People on the site rip on emergency blankets all the time, but do so mistakenly. E-blankets can provide significant insulation, tho particularly when formed into a bag. I have been in several situations using an e-blanket and have found them to be remarkably warm.
I have been researching for an article on exactly this subject. One study I found actually reported a value of up to R-6 for e-blanket. For those interested, I kinda dropped the research a while ago & will have to dig thru notes to find references, or just wait to see if article materializes.
Heat loss occurs in a bunch of ways; we all know that. Radiative heat loss in temperate surroundings ranges from 45-65%. Yup, you read that right.
As many here know, I have a NeoAir and like it quite a bit… but find that it's far too cold of a pad for temps into the low 40s or lower. I think that the reason the pad isn't as warm as numbers seem to indicate it could be is the fact that it is still mostly an air mattress and, just like a "pool toy" air mattress will still have significant heat loss via air movement thru the pad. I've been (purely) speculating that my problems might be worsened b/c I'm using a wide pad and have more open surface area. Dunno.
On the last major trip w/the pad I ended up wrapping myself in a space blanket. I gained at least 20 degrees of perceived warmth. Full circumferential wrap of the e-blanket stops the majority of radiative heat loss, sure, but also stops evaporative heat loss. Oh, no real convective heat loss then, either. But do need the full wrap. B/c my pad is a wide, I couldn't get the blanket wrapped circumferentially around the pad. I feel that enclosing it that way would make it warmer, but I don't know. Experiments to follow. Wouldn't want to wrap the e-blanket over self in sleeping bag and pad, b/c you'll get the sleeping bag nice and damp from your perspiration.
As I've said in several other NeoAir threads, it isn't a winter pad and isn't intended as such. Much data on this site re: necessary ground insulation for comfort in a variety of temps.
Food for thought.Apr 25, 2010 at 2:36 pm #1601904
Ben 2 WorldBPL Member
@ben2worldLocale: So Cal
My experience with NeoAir air pad vs. REI 1.5" Lite Core self inflating pad:
1. I feel warm in my beloved MB No. 3 bag atop my REI Lite Core down to about 30F.
2. Last month, same bag but using NeoAir instead — I could physically feel the cold permeating through all night. Luckily, it was in the mid-30's — so cold but not deathly cold. I would NOT view this as any kind of 3-season pad.
3. Two weeks ago, switched back to Lite Core — slightly colder temps than (2) above — back to feeling warm again.Apr 25, 2010 at 8:47 pm #1602032
Ross BleakneyBPL Member
Rick is right, most of the insulation comes from the air being trapped and a little is from the IR reflection. The NeoAir was a very interesting breakthrough. Previous to it, inflatable pads trapped the air with foam or down (each having their own disadvantages). Pads that have no material were extremely cold, as currents develop inside the mattress. The NeoAir traps the air with the pointy baffles. In doing so, it works like most insulation (such as a down air mattress): it uses trapped air to prevent heat loss.Apr 26, 2010 at 1:12 am #1602089
Sorry Brad if this comes across as harsh but there's a lot of misinformation in your post and I'm a geek, I can't help it.
>The only R-value from the NeoAir is the space blanket inside. The baffles are just randomized poly scrim, if you will… looks kinda like a fabric version of OSB board. Really just to hold the pad together.
The baffles are actually where most of the insulation value comes from. They stop convection currents forming within the mat. The marketing on the NeoAir box is misleading, the fact that the baffles are reflective is a minor enhancement, but people love them some bending red arrows.
>People on the site rip on emergency blankets all the time, but do so mistakenly. E-blankets can provide significant insulation, tho particularly when formed into a bag. I have been in several situations using an e-blanket and have found them to be remarkably warm.
Yes, they keep you warmer when formed into a bag because they then trap air. They are also a vapour barrier so stop evaporative heat loss.
>I have been researching for an article on exactly this subject. One study I found actually reported a value of up to R-6 for e-blanket. For those interested, I kinda dropped the research a while ago & will have to dig thru notes to find references, or just wait to see if article materializes.
This is not possible unless the blanket was formed into a multilayer corrugated blanket like a Blizzard Pack, in which case it is again trapping air.
>Heat loss occurs in a bunch of ways; we all know that. Radiative heat loss in temperate surroundings ranges from 45-65%. Yup, you read that right.
Only if you've already reduced the other sources of heat loss to a minimum
>As many here know, I have a NeoAir and like it quite a bit… but find that it's far too cold of a pad for temps into the low 40s or lower. I think that the reason the pad isn't as warm as numbers seem to indicate it could be is the fact that it is still mostly an air mattress and, just like a "pool toy" air mattress will still have significant heat loss via air movement thru the pad.
Agreed, the NeoAir's baffles help, certainly better than a plain air bed, but they are not as effective as foam or down
>On the last major trip w/the pad I ended up wrapping myself in a space blanket. I gained at least 20 degrees of perceived warmth. Full circumferential wrap of the e-blanket stops the majority of radiative heat loss, sure, but also stops evaporative heat loss. Oh, no real convective heat loss then, either.
Exactly, it's the evaporative and convective (and just plain wind chill) that are the biggies. If radiative was important you wouldn't have to make sure that the gaps were filled to feel a benefit because radiative heat moves in straight lines.Apr 26, 2010 at 10:04 am #1602195
So taking my z-lite and space blanket will probably not suffice for sleeping on snow. I will need my BA insulated air core mattress which is rated at R-4.1. But there are other mattresses rated at 2 or 3, what is the rating considered sufficient for sleeping on snow?Apr 26, 2010 at 11:15 am #1602234
Figure out what the right pad combination is for normal non-snow sleeping, and then double that to use on snow.
–B.G.–Apr 26, 2010 at 11:30 am #1602240
so for instance, i expect the coldest temp to be around 25f. my guess, this would require R-2.5 or so. Now to sleep on snow at this temp, I will need R-5.0? Does that sound right?
That means that my BA Insulated Aircore (r4.1) may not be enough and maybe i should bring my z-lite also for a total of r5.1).
I was hoping not to carry both.Apr 26, 2010 at 11:36 am #1602241
Bradley DanylukBPL Member
My Big Agnes IAC is not warm enough for any sort of snow sleeping for me, even around or slightly above freezing air temperatures. In every instance of snow either in the air or on the ground, I've woken up on the IAC after a few hours shivering because my back is cold and I can feel the heat being sucked down out of me. Even if I manage to stay warm enough, having one side significantly cooler than the other is really uncomfortable and hard to sleep with. I'm not sure I trust the R4.1 rating, or maybe it's just that 4.1 is not really enough for those situations anyway.
I tried sleeping at 30 degrees on snow with another warm body next to me, on an IAC, PLUS a 3/8" CCF on top. It definitely felt warmer than just the IAC, which was unbearably cold, but we both still woke up unable to sleep after 4 hours and had to start a fire.Apr 26, 2010 at 12:43 pm #1602275
Jim W.BPL Member
It doesn't matter much whether the air temperature is -10 or +60. Snow still melts at 32 degrees and if it's melting under you that's because you're feeding it energy.
Inflatable insulated mattresses are nice and cushy. Unfortunately when your pressure points sink in (hips, shoulders, etc)- you lose insulation under that point. I was very cold a couple weeks ago on snow with a 2" thick therma-rest. The next night I added a 3/8" foam mattress and felt 20 degrees warmer.Apr 26, 2010 at 12:49 pm #1602279
It's true that air temperature doesn't directly matter too much in this case. However, if the air temperature is -10 F or +30 F, then that tends to force the surface snow temperature to be -10 F or +30 F. That -10 F snow will suck the heat out of you faster than the +30 F snow.
After I've spent my first night out in the snow, I always assess the effectiveness of my sleeping pad in the morning. If there is a good melted depression where I was sleeping, then that means that my sleeping pad was not good enough. If the surface only is melted, then that is a good sign that I had enough pad.
–B.G.–Apr 26, 2010 at 2:15 pm #1602327
I used my BA insulated aircore and z-lite on snow once, it felt fine in that case with the temp falling to only 35f. So this same setup should work fine even if temps drop down to 25f or 15f?
the surface of the snow I'm sleeping on should be considerably warmer than the surface of the snow outside of my sleeping area since it's insulated from ambient temps and from winds by my mattress, quilt and body. So even if it gets 10f outside, the surface I'm sleeping on is probably around 30f.Apr 26, 2010 at 2:42 pm #1602347
No, I don't believe so. I think you are over-simplifying snow temperatures. In some places surface snow is affected more by air temperatures, and in other places, surface snow is affected more by deep snow temperatures. The people who really understand snow temperatures are backcountry cross-country skiers and ski patrolers who are avalanche-aware. You can get unexpected temperature gradients through a snowpack, and that makes for unstable snow layers, and those lead to avalanches.
I've just found that sleeping on snow requires about double the sleeping pad that I would have used for non-snow.
–B.G.–Apr 26, 2010 at 3:09 pm #1602369
Okay, so like many other aspects of UL, a simple and reliable calculation based on conditions expected is not really possible/practical. Too many variables and too many difference of opinion.
I'll just adopt a random system like most of you veterans are using, experiment with it in the field, learn the hard way what works for me, and develop my own instict for guesstimating what might work for future trips. I'm comfortable with that. I hate math anyway!
For now I'll just take both my mattress and CCF, and if I freeze my butt off, I'll do some situps and come up with a better system next time.Apr 26, 2010 at 3:26 pm #1602380
Ben 2 WorldBPL Member
@ben2worldLocale: So Cal
Doesn't Richard Nisley have a chart for all this?Apr 26, 2010 at 3:34 pm #1602387
Rick DreherBPL Member
@halfturboLocale: Northernish California
I appreciate your frustration–definitive answers aren't easy to come by considering the vast number of variables. If I may make a suggestion, select a foam pad to provide warmth and add a mattress for comfort. For me a full-length foam pad and shorty air mattress is the best cold weather system for the least weight. The downside is foam pads are bulky, even if they're light, so are bothersome to haul. But a shorty NeoAir is a tiny thing that almost gets lost inside the pack.
FWIW I find the NeoAir more comfortable and marginally warmer than the insulated BA-POE mattresses. This in one area we've seen advance a lot the last few years.
RickApr 26, 2010 at 3:36 pm #1602390
Travis LeannaBPL Member
Richard's got a chart for just about everything. He even has a chart about his charts. : )
I do remember Richard saying R-values are cumulative. 4.1 for the BA plus whatever the Z-lite is. You want about an R-value of 5 or greater to stop the transfer of heat between your body and the ground.
Adan, I've used a BAIAC on snow and/or down past 15 degrees. Most of those times I was a bit chilly because it was inadequate winter padding, but I was ok for a few of the times.
If you paired a CCF with a your BA pad, as long as your insulating layers and bag are appropriately rated, you'll probably be quite find in the teens and single digits. But I have no experience sleeping out when the mercury drops below about 10 F.Apr 26, 2010 at 3:42 pm #1602394
Jim W.BPL Member
Actually I agree "one R-value is good for virtually all snow camping". I just had a shocking reminder last weekend after forgetting that fact. In colder conditions the snow stays below freezing and provides some insulation. In warmer conditions the snow is probably icier and conducts heat more- but it isn't as cold.
The most important thing I want to emphasize is that an inflatable insulated air mattress provides comfortable padding because it compresses under your pressure points such as hips and shoulders. Unfortunately it also becomes cold at those points unless it's quite thick.
So my bottom line is either layer a closed-cell foam pad under your inflatable, or make sure the inflatable keeps you well off the snow.Apr 26, 2010 at 3:47 pm #1602397
On a related topic, I tended to see the highest failure rate in air valves and such when the temperature got the lowest. We all keep such systems tested for normal temperatures, but when it gets really cold and you need the insulation the most, that is when the failures occur most. As a result, for snow camping purposes, I never rely on an air-filled anything for more than 50% of my sleeping pad. Quite commonly, I will have one Thermarest plus one CCF pad.
–B.G.–Apr 26, 2010 at 6:39 pm #1602484
Robert BleanBPL Member
@bleanLocale: San Jose -- too far from Sierras
No, I don't believe so. I think you are over-simplifying snow temperatures. In some places surface snow is affected more by air temperatures, and in other places, surface snow is affected more by deep snow temperatures.
Are you sure? Since properly packed snow (i.e. not overly compressed) is a pretty good insulator, I would expect the snow under you to soon come to some equilibrium temperature, and then not transmit an awful lot of heat.
This is assuming that you are not camping on ice, or hard-packed snow (such as boot-packed).
–MVApr 26, 2010 at 7:08 pm #1602496
Bob B., I don't know what part of California it is where you snowcamp, but I've been all over. The only generalization that I can make about California snow is that I can't make any generalizations about it. Often, we do boot-pack or ski-pack the snow before setting up a tent or digging a snow cave. Yes, I would expect the snow directly underneath your sleeping pad to arrive at some equilibrium temperature, but that temperature is fairly unpredictable. You might have cold snow below and soft ice cream on top, or vice-versa. You don't know whether the water will be rising upward or sinking downward. We camped in Yosemite one time, and all of a sudden in the middle of the night, I started hearing noises and feeling collapse underneath me, and my sleeping bag and pad dropped about an inch. It was shallow depth hoar that had collapsed.
–B.G.–Apr 27, 2010 at 10:13 am #1602756
Andrew, most of your comments mirror my own, so I guess most of your thoughts are also misinformation?
One thing that you're right about is that the baffles do contribute–even significantly–to the warmth of the pad. However, your statement "the fact that the baffles are reflective is a minor enhancement" is patently incorrect, because the baffles are not reflective. For those curious, the radiant heat barrier of the NeoAir only accounts for approximately 25% of the R-value of the pad. Cascade tested the pad as just the shell w/the baffles, no radiant barrier, and found an R close to 2. I was quite surprised to learn that. My personal feeling is that the baffles do a lousy job controlling convective current transversely. Apparently that is some concern, & although entering the realm of "hard to tell," a Cascade employee has concurred w/my previously expressed thoughts that you do have some extra heat loss thru the sides… but which can be mitigated by use of a tent or a narrower pad with a sleeping bag that overhangs the edges of the pad to keep the heat in. My problems occurred w/a wide pad and a narrow bag under a tarp.
Please note that your comment "Yes, they keep you warmer when formed into a bag because they then trap air. They are also a vapour barrier so stop evaporative heat loss." echos exactly some of my comments.
On "This is not possible unless the blanket was formed into a multilayer corrugated blanket like a Blizzard Pack, in which case it is again trapping air," re: the R-value, apparently some testing has found that it is possible. If I recall correctly, however, those tests were done in a different context, that of building materials & construction. If I can find the references, as I stated originally, I will post them. I have owned and used a blizzard bag (actually MPI) and it is quite remarkable. But it is a different matter.
"Only if you've already reduced the other sources of heat loss to a minimum," Um… Yeahhhh. That falls into the category of "Duh."
I do appreciate folks comments about the baffles, because it made me do some more research and I found that they do contribute more significantly to the insulative value of the pad than I originally thought. Ie, I was wrong about the radiant barrier being the primary warmth. I've had one the pads cut apart in my hands, investigating it closely, and could not discern any practical R-value in the baffling. Just goes to show ya!
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