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Topic: Thermal dynamics question, Clothes related< Next Oldest | Next Newest >
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hikerjer Search for posts by this member.

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PostIcon Posted on: Dec. 07 2013, 5:30 pm  Skip to the next post in this topic. Ignore posts   QUOTE

I've always been under the impression from reading and talking to knowledgeable people in the field that more than anything it's the thickness, loft, if you will, of clothing and sleeping bags that determine their warmth.  That is, given that the material is dry and not next to your skin where conductive cooling can take place, four inches of down really isn't any warmer than four inches of wool, cotton or steel wool for that matter.  It's the loft. Of course down is infinitely more preferable because of it it's weight and compressibility but really isn't any warmer. Therefore, I'm always somewhat puzzled by manufacturers' claims that they have a new thinner, lighter and warmer material. I don't think it can be unless there's some sort of independent warming mechanism i.e. electricity, in the material.  What's your take on this?

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PostIcon Posted on: Dec. 07 2013, 5:47 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

It's not entirely that simple.  The air within the loft has to be dead air.  If it has freedom of movement, it allows internal convection within the insulating layer that allows heat to move to its boundaries, and from there to be lost by any heat transfer mechanism.  A thinner layer of truly dead air can be warmer than a thicker layer that isn't as stabilized.  However, there are definitely limits, and I'm dubious of high R-value claims for very thin layers.
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llamapacker Search for posts by this member.

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PostIcon Posted on: Dec. 07 2013, 5:52 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

I don't want to argue with the knowledgeable people in the field, but I think you may be confusing insulation and warmth.  Warmth is generated by your body and the role of insulation is to retain as much of that heat as possible.  

Talk to your people about the three ways heat is transferred: radiation, conduction, and convection.
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hikerjer Search for posts by this member.

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PostIcon Posted on: Dec. 07 2013, 6:15 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE


(llamapacker @ Dec. 07 2013, 5:52 pm)
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I don't want to argue with the knowledgeable people in the field, but I think you may be confusing insulation and warmth.  Warmth is generated by your body and the role of insulation is to retain as much of that heat as possible.  

Talk to your people about the three ways heat is transferred: radiation, conduction, and convection.

You're point on warmth vs insulation is well taken and I understand that.  Matter of semantics but your take is the better of two.

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PostIcon Posted on: Dec. 07 2013, 7:13 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

I'll echo what big_load said.  Air is an excellent insulator as long as it can't move.  What we generally call "insulation" is mostly designed to entrap and immobilize air.  Generally speaking, a denser insulation will do a better job of holding the air still, but if it gets too dense then its own conductivity can start to work against it.  Fine steel wool, for example, might entrain air very well, especially if you pack it real tight, but then the conductivity of the steel will overwhelm the benefit of the entrained air.

So the challenge for clothing and bag designers is to find insulating materials that have the best combination of low conductivity, low weight, good immobilization of air, minimal thickness, acceptable cost, etc.  There ain't no free lunch.
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PostIcon Posted on: Dec. 07 2013, 7:39 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Okay, sorry, I didn't intend to be nit-picking.
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Walkinman Search for posts by this member.
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PostIcon Posted on: Dec. 07 2013, 8:57 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

What big_load said .. insulate properties vary from one material to another.

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PostIcon Posted on: Dec. 07 2013, 11:27 pm Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Aerogel...

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PostIcon Posted on: Dec. 08 2013, 12:08 am Skip to the previous post in this topic.  Ignore posts   QUOTE


(Tigger @ Dec. 07 2013, 8:27 pm)
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Aerogel...

WAAAYYYY too heavy for clothing, but it does have fantastic insulating properties!  On the other hand, if you want the best insulating insoles on the planet....
http://www.amazon.com/MCR-Saf...._shoe_1


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