Apr 8, 2011 at 4:34 am #1271896al bBPL Member
As you move away from the heatsource (your) body convection current loss presumably becomes less important, so insulation structure could be graded accordingly:
to save weight (and/or cost)?
eg Primaloft on inside, coarser wadding on outside?Apr 8, 2011 at 7:43 am #1721893Aaron BensonMember
@aaronmbLocale: Central Valley California
It seems to me that one would save cost by moving to lesser quality/grade materials. But, weight could certainly go up, depending on the materials used. A distinct advantage of quality insulation is its lighter weight–hence the price, of course–so while costs can be saved on the one hand, it still seems like a give-and-take situation: cost or weight?
On the other hand, though, with quality (sufficient?) insulation throughout, perhaps one's body can more efficiently stay warm, as it wouldn't be attmpeting to compensate for cold(er) extremities?Apr 8, 2011 at 9:07 am #1721935David DrakeBPL Member
@daviddrakeLocale: North Idaho
The only low cost/low weight/low quality insulation I can think of is air. When air mats incorporate a thin layer of insulation (eg POE) or when people use a thin foam mat with a NeoAir, that might be similar to what you're thinking.
It's an interesting thought. It also seems like down in a bag or quilt will compress a bit under its own weight, so there might be a gradient there: from denser near the body, to fluffier next to the bag's outer shell.
Also, I don't know if it would matter in practice if the better insulation was closer to the heat source (the body) or the heat sink (the ground or cold air). I've never used a foam pad/NeoAir combo–I always assumed the foam was placed on the bottom next to the ground, but maybe not?Apr 8, 2011 at 9:36 am #1721948carl beckerMember
@carlbeckerLocale: Northern Virginia
Interesting thought but my setup would be a wool cap/pullover/pants then down inner jacket then down bag for the coldest times as that is what works layer wise for a total trip. I suspect down is a better insulator than wool. Interesting also is the fact that some dogs have a second inner coat to help insulate which may very well be a better insulator closest the body.Apr 8, 2011 at 10:10 am #1721964EndoftheTrailBPL Member
Maybe not understanding or answering the question…
To me, if minimum bulk and weight for a given warmth are the goals, then one would use the most efficient insulation, period. For example, let's say 10 ounces of 850FP down is needed underneath a wp/b shell. I can't see how one can substitute the insulation layer with two instead — and achieve the same efficiency (warmth to weight and bulk ratios) — such as substituting with just 7 ounces of 850FP — and then a cheaper insulation farther away from the body, such as 500FP down, or fleece.
Conversely, I am thinking that if two layers of insulation — a good one near the body and a coarser one farther away — are enough for a hiker at a given temp — then that hiker can likely shave bulk and weight by replacing those two with just one higher efficiency insulation??Apr 8, 2011 at 3:26 pm #1722152al bBPL Member
My idea was more that the outer insulation could be sparser(lighter) becuase less convection currents means plain air is more insulative in bigger "chunks",Apr 8, 2011 at 4:02 pm #1722165Todd TBPL Member
@texasbbLocale: Pacific Northwest
I'm not sure what you mean by "quality."
If you mean insulating ability (R-value), it doesn't matter at all the order in which layers are applied–only the total R-value matters. There may be considerations related to compressibility (e.g., don't put down on the inside because the weight of the next layer might compress it). And there could be other things going on like air leakage between layers or the location of condensing planes within a layered system, but those are separate matters I think.
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