Question of the day?

You are getting cold due to the heat loss via the B/A Insulated Air Core because air is a conductor of heat/cold.

The air pad is acting as a heat sink to draw away the warmth from your body.

When you are on your side you feel warmer because there is less surface area in contact with air pad, therefore you are losing less heat and feel a little warmer.

I had this very thing happen in Yosemite while sleeping in a tent with my wife.

I had a Marmot Helium 15 degree Bag and a Prolite 4 and a blue foam pad.

My wife had a BA air pad and a 20 degree synthetic sleeping bag and woke me up literally with her teeth chattering.

I thought it was her sleeping bag and we exchanged sleeping setups. (The things we do for love).

She quickly warmed up and was snoring away peacefully.

After falling asleep, I woke up in about an hour with my back icy cold.

I deflated the BA by 50% and was immediately warmer.

Soon after, I let almost all the air out of her pad and immediately got warmer and was able to sleep.

P.S. You described the exact situation we encountered last year.

-Tony

Agree with Tony. Isn't the BA pad supposed to be used with the primaloft on top also? Even so, it may simply not have been enough and needed closed cell foam in addition.

Hi Tad

Hey, what's with all this 'you' stuff? I gather this happened to you, not me? :-)

OK, I have had something similar happen to me once. I was field testing some rather weird Zyflex thermal pants for BGT at the time, and my legs were getting rather cold in my SB. I knew they should not be cold in the conditions.

Eventually I took the thermal pants OFF, and warmed up.

The problem was the 'thermals' were just a bit too weird, and tight, and they were restricting the circulation in my legs. When I removed them the circulation was restored to its normal level, and my legs warmed up.

I see you had lots of clothing on. I suspect it was all too tight for sleeping. Maybe the pad was not warm enough, but it is meant to be insulated. I would finger the excess clothing.

We always advise girls to remove their bras when sleeping – partly for the same reason. Anything tight is going to restrict circulation.

Cheers
Roger

Was the underclothing sweaty when you turned in?

It does sound like the pad … except that the BA alleges an R value of 4.1 for the Insulated Aircore … more than other light weight alternatives

How do you find the girth of the Marmot Hydrogen? If it is marginal for you, it and the down sweater may have their insulation compressed

How about fuel (was your food intake adequate)? More than you needed for the day's hike I hope.

A combination of Roger C's tight clothing and Roger T's sweaty clothing could be the answer. I was once on a ski tour where we camped in temperatures down to -25C/-13F (I think it Celsius when I saw the 24 in the question I immediately thought "that's warm"!). One of the party had a much thicker down bag than the rest of us and slept in all the clothes he'd been skiing in and wearing in camp, including some thick stretchy wool mix salopettes. Despite this he couldn't get warm enough the first few nights. There were three of us in the tent and he was the only one cold despite having the warmest bag. I suspected the salopettes were holding moisture and sure enough they felt damp to the touch. It was only after a few nights shivering that he agreed to try sleeping without them – he found the idea he could be warmer wearing less hard to accept. He then slept warm. The salopettes were close fitting so the tightness could have played a part too.

That's a lot of layers, top and bottom. On the bottom it does sound like it might be pretty constrictive. Were the Ibex both dry, ie sleeping layers? If so, you shouldn't have needed most of the extra layers. Maybe the down jacket, although I'd probably drape this over me in the bag, for best insulation value.

I wouldn't trust a BA IAC for those temps, just in case I ended up on snow, so I carry a 1/8 EVA pad to put on top of the BA if there's any chance I may end up on snow. ( I realise you weren't sleeping on the snow)

Okay, there's the problem, how do you fix it.

Eat more. Same thing happened to me last weekend. I was on a callout and realised I'd undercooked my bag for the conditions. I was planning on a low of 8C (45F) and took my optimistic MH Fairview 40. I realised about 5.00pm I was going to be cold. Fortunately the Police were catering, so I went for the second big serve of roast beef and turkey with roast veg and gravy plus a side of cheese vegies. Add in a couple of desserts and three hot chocolates, and I had to peel off my thermals an hour after I crawled into my bivvy. I was steaming in there, but the tarp was iced up, so it was at least 0C or lower. Lots of fat is your friend. Take a Snickers to bed with you if you need to.

Next is position. It's a whole lot colder out in the open than it is under a tree. A leafy, dense tree will give you at least another few degrees in reduced radiant heat.

And then, if you're waking up cold, you need to add in some extra heat to your bag. The fastest way to do this is to do some sit ups, in your bag. You're already miserable, so why not? Otherwise crank up that stove for a warm drink, and a hot water bottle to go between your thighs. You'll get colder doing this, but it's much nicer than doing sit-ups.

Tony nailed it! I use an air mattress pad also (POE Max Thermo 3/4 length). Love it for the comfort BUT I have to add CCF pads as the temp drops.

P.S. Don't believe the marketing dept when they talk about 'R' values!

A couple of things I need to explain before I give my answer (that I forgot to in the question):
Roger- the you/I part was so I could look a little obscure (meaning to hide how inept I was in this scenario).
Everyone- I added the layer as I got colder. I was not at all sweaty. I was hiking with just the Ibex, wind shirt and OR pants without thermo bottoms. I was neither cold nor hot, it was just right.
My bag was a Marmot Helium 15* (not Hydrogen, I have both) with plenty of girth for what I was wearing. In fact I pulled in the sides with my hands to see if I was trying to heat to much space.
The layers are each are little larger then the one under it- I do this so I can get this kind of layering if needed.
Food- I eat 2 fully stuffed burrito’s (Sarah’s recipe), just before bedtime. I don’t think I could eat any more.

My Answer:
I think Tony was spot on. I have slept in the same situations with the same bag, far less clothing and was toasty. The only difference was I was on a old standard Thermorest.

The Aircore was the only change in equipment.

I did feel warmer on my side, though I can't sleep that way. I think this was because of less contact with the pad.
At about 5:00 am I was trying to figure out how to get warmer and remember the I was using a space blanket (the real thin kind) for my ground cloth. It is very used and half of the sliver is warn off, but I thought maybe it could still radiate some heat up. So I put it between the Aircore and the bag. I think I noticed some difference, maybe it was because I was so tired.
I don’t think I’ll ever use the Aircore in Low temps again unless I take something substantial to go over it!
It is good to see that I’m not the only one out there that has “issues” with their equipment.
Thanks everyone for your responses- I’ve learned a number of things that can effect my temp/comfort and the possible solutions.

Tad,

Having going the the Sierra's Club's Snow Camping course, I found that a lot of the instructors are big fans for the Exped Downmat 7 to give them the comfort of an air mattress while staying warm.

My friend, Jeff, who was also on the trip that I spoke of switched to a Exped Downmat 7 since that trip and has been a warm and happy camper since.

If you like the comfort of an air mattress, you might want to give it a look.

-Tony

> I have slept in the same situations with the same bag, far less clothing and was toasty. The only difference was I was on a old standard Thermorest.

In that case, I wonder whether a better solution might have been to put the extra layers of clothing under you? Either on top of or under the BA mat? A substitute for the foam mat.

As for the Space Blanket – forget it. There would be minimal radiation loss under you, and the conduction insulation it would give would be ~zero.

Cheers

I've slept on this same pad in low teens wearing only my trekking layer and in a 10 degree down bag and was quite toasty. This was in the Smokies and there was dry ground but we did experience snow and hail over night. I'm a warm sleeper though so that could account for some of it. The pad is rated to 15 degrees I believe.

Tad,

Based on your post, I just tested a BA Insulated Air Core. I have a prototype insulation tester that I designed and built. I used the best case environment of full inflation and a sheet on top of it to simulate being completely covered with a sleeping bag. Contrary to my expectations, the test yielded an R Value of 3.987. This is effectively equal to their 4.1 spec.

In their advertisements, they state a comfort rating of 15F for their 4.1 R Value. My calculations yield a comfort rating of ~44F and an Extreme rating of ~15F. An Extreme rating is defined as ~6 hours of sleep before you wake up shivering do to a progressive drop in your core temperature.

By contrast, the old Thermarest Standard had a vendor rating of R Value 5.0. Independent lab tests yielded and average of R Value 4.84. I recently tested the GG ThinLight 1/8" and its .45 rating matched my results. It would take two ThinLights in combination with a BA Insulated Air Core to provide equivalent insulation to the old Thermarest Standard.

You could also augment your BA Insulated Air Core with a 1/4" pad but, two 1/8" pads would be warmer do to the contact resistance between the foam pads.

Thanks for the continued responses-
Roger- I never thought of putting the clothes under me. I don't know If I could have laid them out and stay exactly over the pattern made, it would have been better then what I had. I also think the space blanket was a placebo. During the night when I was cold I was willing to try anything.

Chris- The ground had frost heave about 1 inch thick and had been that way for a couple of days- the ground was as cold as the air. I don't know if these conditions were different then yours but it made a huge difference for me.

Richard- As a builder I work a lot with a lot with R-values. I also understand the variables that go into play outside the straight numbers. It's to bad we can't put a blower door test on this type of system to test how it really works. From my experience 2 days ago, it would fail. The pad, regardless of the R-value sucked the heat out of me at 24F degrees. I wouldn't use it below 40F.

Tony- I looked into the Exped down mat, but the price was to high for me. I guess if it really works it isn't that expensive. Though it is a little heavy. I'm still not totally sold on an air mattress (I hate blowing them up).
Though I think they might help me sleep better.

This has been quite informative for me, thanks again.

Second law of thermodynamics. Inside the air mattress convection (Bernard Cells) occurs because of your body heating up the moist air, which moves the cold air on the bottom side of the pad to the top. Thus, lower temperatures next to your body. Convection doesn't occur in a solid material (closed cell pads), so your body's heat won't run away from you.

As I commented earlier, I need appropriate thickness of CCF pad in conjunction with the air mattress. But, if I die in my tent and rigor-mortis sets in, I can guarantee you that I will be clutching my air mattress and they will have to bury it with me. They are too comfortable to give up!

Tad,

I am with you…the pad is very expensive and I just don't care for sleeping on an air mattress.

I prefer something firmer.

One nice aspect of the Downmat 7 is that the stuff bag is a billow that is used to inflate the air mattress.

Having down inside the air mattress, inflating it with your lungs collapses the loft and the down.

And yes, it is heavy.

Just thought you and others might want the extra info.

So what is the next question everyone?

"If a backpacker takes a 4 lbs. Dura-flame log into the back country, how many stokes on a mini-fire steel will be needed to ignite the Dura-flame log?"

-Tony

Tad,

I used an inflation bag to fill the mattress I measured the R Value on. Did you inflate your mattress by mouth?

Max,

If the Primaloft Sport substantially fills the air mattress cavity, the convection is negligible as it is for CCF. Conduction and radiation losses will occur in both sleeping pad types. The R Value rating reflects the composite of convection, radiation, and conduction heat transfer.

Hi Tad

> I don't know If I could have laid them out and stay exactly over the pattern made,
My thoughts too. But if you had laid your bits of clothing out on the ground and covered them with the space blanket, and put the air mat on top, I think they might have stayed in place. I'd focus on your torso area.

Me, I use a slightly heavy (780 g) 2" thick Therm-a-Rest – no longer in production though. (That's a worry!) I use it on snow happily, and find that the outside temperature does not matter very much to the mat. The snow directly under it warms up to just sub-freezing, and is a good insulator.

Sleeping on cold ground – that is actually colder than sleeping on snow imho.

Cheers

Roger,

I've tried the BA IAC on snow, with the additional mat above the BA and below. When I tried it below, I had the full length 10mm cheap blue mat under the tent to try to reduce condensation on the tent floor. I was in an Olympus with one other person. I was warm enough, but only just, but from about mid calf down my legs were cold. when I checked in the morning, the foam mat had folded when I placed it, and the calf section corresponded to the cold leg section. I'm not sure whether this also acted as a heat sink for the rest of the mat, pulling heat out generally.

The next time I placed a 3mm EVA mat on top of the BA. This is a higher density EVA, used to cover insoles, that I purchased from work. It is only 150cm long (60") I used my pack as a pillow. I was in a Megalite, on my own with enough wind to snap a couple of poles on an old Olympus camped with me. I was warm all night.

Temps both times were just below 0C.

I believe the thinner pad, on top of the BA, provides much better insulation for the weight, as would makeshift insulation such as a pack or clothing. I do intend to add some kind of elastic, velcro or toggles, to make it easier to keep in place.

>In that case, I wonder whether a better solution might have been to put the extra layers of clothing under you? Either on top of or under the BA mat? A substitute for the foam mat.

As for the Space Blanket – forget it. There would be minimal radiation loss under you, and the conduction insulation it would give would be ~zero.

>Max,

If the Primaloft Sport substantially fills the air mattress cavity, the convection is negligible as it is for CCF. Conduction and radiation losses will occur in both sleeping pad types. The R Value rating reflects the composite of convection, radiation, and conduction heat transfer.

Richard,

I'm pretty sure the Primaloft doesn't substantially fill the cavity. My understanding and experience is that it's a fairly thin blanket of insulation, attached to the top of the pad (the side with the writing printed on it)

When I feel it in an inflated pad, it seems to be about 3/4 to an inch thick. This would explain Tony's experience with deflating the pad, although I would expect 2/3 deflated to be warmer than fully deflated. I find it more comfortable, as opposed to warm, to not full inflate the pad.

Rod

Richard, I inflated it by mouth, as far as I know that is the only way to inflate this B/A pad. I also recall that I had an excessive amount of moisture around my lips and mouth piece of the pad. To the point of being bothered by it.

Tad,

Mouth inflation will definitely lower the pad's insulation value relative to the dry air inflation method I used for my test. I guarantee you that BA didn't blow up their mattress by mouth to test R Value 4.1.

I use the BA Pumphouse Sleeping Pad Pump & Dry Sack for both for lab testing and field use. It weighs 1.5 oz and does multiple duties as my stuff sack, inflation sack for my Alpacka raft, source water bag for my gravity filter, shower sack, and pillow.