[pct-l] Layering

[Bill Burge]

Sorry for taking this one all the way back to the beginning, but there  
was one comment I wanted to address:

> If it is the air between the layers more than layers themselves that  
> produce warmth...

This is not true.  It is the air trapped in the layers, more than the  
air between the layers, that provide insulation.  http://www.askthebuilder.com/How_Does_Insulation_Work.shtml 
   The paragraphs starting with "Conduction" and "Convection" and the  
couple after that are the primary ones.

This is why large chamber (uninsulated) air mattresses (think pool  
rafts) are some of the coldest ways to sleep.  They have only a single  
layer of the precious insulation of air and are thus a bad source of  
insulation because they suffer from convection and conduction.  You  
want a material that conducts poorly, like down or fiber fill, to  
prevent the convection of the air, since it conducts heat even worse.

Also, insulation does NOT "produce warmth" it only prevents it from  
moving too far away from you.  If you are not producing enough warmth,  
adding insulation will not help you that much.  It "traps" heat.

It also helps if you understand that from a physics point of view,  
there is no cold - only "heat" and "less heat".

BillB



On Dec 21, 2009, at 2:03 PM, Amanda L Silvestri wrote:

> Okay, here is my thinking.  If it is the air between the layers more  
> than layers themselves that produce warmth, would the following work?
>
> 1.  A light weight sleeping bag and perhaps two silk bag liners  
> instead of just one.
> 2.  Two layers of base layer, the outer size larger than the inner  
> layer.
>
> It's the air between the layers, right?  Has anyone tried this.  I  
> haven't seen it mentioned.  It seems to me that this could save  
> weight and expence.
>
> Shepherd
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