(warning, long post. Main points in bold you can just skim and read them)
I meant to post about this a couple of months ago when it happened, just never got around to it and/or I forgot about it. I was hanging my Superior Gear insulated Hammock(SGIH) on a cool, but very breezy, day. Nowhere near cold enough to test the rating of the SGIH, but there was a wind chill adding to the challenge. No tarp or sunshine, over cast day.
So, I hiked in wearing a cotton shirt and jeans, I don't recall if I was wearing my thin fleece jacket or not, or if instead I had it in the pack. But I was not wearing it when I lay down in the hammock. Since I was a good 10 or 20+ degrees above the rating, I immediately felt that glowing warmth that so many of us report with down insulation, particularly UQs. Especially compared to an uncomfortably cold back without it, particularly when the wind gusted.
But after I had laid there a little while enjoying my toasty warm back, I realized that top warmth was becoming a problem, as the wind was getting to me. So I get up and put on my fleece jacket, and to my shock and amazement, I do not feel that immediate backside warmth!
Now, this was a real shock to me, because I have always been a layering kind of guy. Many is the time that I have used various quilts way below their rating, and been toasty warm, and I have done this by adding either layers of worn insulation or vapor barriers. Now I do not deny their personal experience, I'm sure that is how it has worked for them, but my experience has always been sort of the opposite of the "sleep naked or close to it" group. There are quite a few folks out there who have either removed layers and warmed up, or started with fewer layers and then been warmer with a given quilt than they were wearing extra insulation. Most of them seem to feel that wearing extra insulation keeps your body heat from warming up your quilt (and I agree with that part, it does) which then prevents your quilt from warming you up. Or something like that. So I've never understood how that works, and I have always added layers of clothing to boost the warmth of my quilts, not to decrease it. But still their experience is what it is. HYOH!
So imagine my surprise when I got back in wearing this poorly compressible fleece jacket and did not feel that wonderful warmth on my back. Certainly not cold, but that pleasing sense of warmth was gone. Now, my topside warmth improved quickly and dramatically. But my back was just not as warm! I have never believed that my goal was to warm up my quilt, but rather to as efficiently as possible keep my body heat from leaving my body. But here I was, with a back that was not as warm! Had my layering approach been wrong all these years? Did I really need to use my escaped body heat to warm up my quilt first, before it could return the favor and warm me up? I was starting to wonder!
So maybe 10 or 15 minutes went by as I lay there pondering this question, but otherwise enjoying my windy hang in the woods by a pond, before my back was absolutely as warm as it had been. In fact, even though the temperatures were not challenging for the SGIH, I even suspected that I was even warmer on my back. Just as I know for sure that was on top. So this thought occurred to me: my fleece jacket was indeed insulating me not just from the cold wind blowing over my top side, but it was insulating me from feeling the warmth in the hammock's built in insulation. Which naturally was also insulating my body heat from leaving my body, and slowing down the rate at which my body heat warmed up the under quilt. Which of course, as far as maintaining body heat and vastly slowing down the approach towards hypothermia that comes from the loss of too much body heat, was not a problem. My core temperature was as warm or most likely warmer, and also my backside was as warm, as it had felt without the jacket. Except now, any lost body heat that has been trapped inside the UQ/SGIH and was radiating back towards me, was busy warming up my fleece jacket rather than my skin. So it took a while to get thru to my skin. Also, my loss of body heat was slowed down by the jacket (thus remaining inside me and/or at my skin) thus not warming the quilt as fast. The quilt didn't get the heat because I still had it myself. At least for a little while.
So, I don't think I was less warm (as far as retaining body temperature goes) with the jacket, nor did I hamper the UQ from doing what it was supposed to do: reduce loss of body heat to the ambient air even more so than the jacket was doing. And sure enough, I was very soon equally and probably even more toasty than I had been before adding the jacket. The jacket was doing exactly what it was supposed to do: slow down the loss of body heat which could then get slowed down even more, and some of it get trapped (hopefully all of it) inside the quilt. By insulating in both directions-my body heat trying to reach the quilt and whatever heat was already in the quilt trying to reach me-the jacket prevented me from warming that quilt up as fast and it prevented me from feeling the heat that the quilt was now containing. But, I still had more body heat/core temp which had not left my body. And I still think that's where I want to keep 100% of any body heat if possible, at least until the point where I start overheating. Then I want to get rid of some of that body heat, but not necessarily into a quilt. At the point of overheating, I'd just as soon the heat travel on out into the atmosphere.
A few weeks later, I feel like I confirmed all of this theory on a trip to the North Carolina mountains, sleeping in the same insulated Hammock, at least 5° below it's and the TQ's rated temperature, + some wind chill- once again, no tarp. (I've got another thread regarding that night) I layered up, and I burned up. I was way too warm. I definitely had to remove some layers, not in order to warm up, but to cool down to a more comfortable temperature. I was in need of losing/getting rid of some of the body heat that I was generating. And those layers I was wearing were definitely not interfering with the ability of the quilts I was using to keep me plenty warm. In fact, quite a bit too warm. Probably in danger of sweating and dampening the down.
OK, the "sleep naked" gang can let me have it, I probably deserve it! But again, I don't doubt your personal experience, even if I don't understand how it works, from a physics standpoint(unless we are talking about over heating leading to sweat). It is just the opposite from my experience. Although now, I also can say I put on an insulated jacket and felt colder. I did not feel that luxurious warmth radiating back from my insulated hammock. At least not for awhile, not until I did, and then I felt at least as much.
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