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big agnes mummy style mattresses
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paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Prof. Nisley on 05/19/2005 01:52:47 MDT Print View

Many thanks for your explicit explanations. I'm guessing you have more knowledge to share. Look fwd to more if you are so inclined.

Again, many thanks,
pj

Jim Ells
(ellsfamily) - F
Heat Loss 101 on 05/19/2005 05:12:15 MDT Print View

Richard, thanks for the insight. I had no idea I could be a 'test subject', but I certainly understand my situation and the overall dynamics of why we get cold. I have a Ridge rest pad that I use for the frame in my Gossamer Gear Mariposa, so I guess when I'm on the trail I'll stick that under my torso. That will be the next test this weekend.
Keep typing lessons, we all need to learn this in order to enjoy our trips and be warm and safe.
Thanks, Jim Ells

Richard Sullivan
(richard.s) - MLife

Locale: Supernatural BC
Emissivity on 05/20/2005 22:10:08 MDT Print View

Hey anybody remember Olivia Newton John?

Let's get technical, technical, I wanna get technical, technical...:))

Isn't radiant heat loss a reality with darker coloured fabrics, due to the fact that the emissivity climbs towards 1.0 as the material becomes "blacker"? i.e Black materials are more transparent to infra-red than visible light is?

Based on this sketchy remembrance of thermal physics, I think that perhaps a mattress such as the BA IAC could indeed benefit from a little reflective mylar (space blanket or Reflectix), especially since it's black.

Over to you Richard N.!

Jim Colten
(jcolten) - M

Locale: MN
color and emissivity on 05/21/2005 06:43:43 MDT Print View

What your eye sees as darkness in a material is an indication of the material's
albedo for visible light.

Radiant heat loss is due to infrared radiation

Thermal emissivity is a measure of how well a material emits/absorbs infrared.

A material does not have to be visually dark to have high thermal emissivity. Perhaps the best common example is snow, which is not at all dark but has thermal emissivity greater than 0.9

Edited by jcolten on 05/21/2005 09:17:49 MDT.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Emissivity on 05/21/2005 12:07:07 MDT Print View

Richard S said, “Isn't radiant heat loss a reality with darker coloured fabrics, due to the fact that the emissivity climbs towards 1.0 as the material becomes "blacker"?

The short answer is “No”.

The long answer is that color has no affect on the long-wave radiant heat loss from our body. Color is only a factor in the absorption or reflection of visible light energy. In sunlight black will absorb most of the visible light energy and covert it to heat energy. In sunlight white will reflect most of the visible light energy and consequently be much cooler.

Our 95F skin temperature generates long-wave infrared energy and not visible light energy. The higher the source temperature, the shorter the IR waves emitted from the material will be. Reflective Mylar will efficiently reflect visible light energy, long-wave IR energy (95F source heat from your body) as well as short-wave IR energy (11,000F source heat from the sun) only if there is a sufficiently large air gap between the Reflective Mylar and the heat source. When you lay directly on reflective Mylar there isn’t a sufficient air gap to reflect the long-wave IR.

Now if Richard S. could figure out a way to levitate above the reflective Mylar without adding a lot of weight to our backpacks, that would give Olivia something to sing about.

Edited by richard295 on 05/21/2005 12:12:43 MDT.

Richard Sullivan
(richard.s) - MLife

Locale: Supernatural BC
levitating above reflective Mylar on 05/21/2005 12:49:06 MDT Print View

Thanks Richard, yes I did figure that out I think! Big Agnes should install a layer of metallized mylar film within the IAC mattress. My assessment of the mattress is that the PL2 layer is probably only 1.8 oz/sqyd, very thin indeed and probably not blocking all the radiant heat loss. Doesn't it seem that a reflective layer could provide significant benefit at very little extra weight?

And I bet Olivia can outsing Agnes :)

Jim Ells
(ellsfamily) - F
Big Agnes IAC and heat loss on 05/29/2005 04:13:43 MDT Print View

As I promised to do, I have now used my 'frame sheet', about an 18"x20" piece of Ridge rest mattress for an additional torso insulator between my back and the IAC in the sleeve of my Mica bag. I have slept well and not gotten the early morning chill in my back. Another case of "multiple use" in an item. So, I'll just slip it in on cooler nights when necessary.
Jim Ells

Brian Griffith
(03bart)
Interesting... on 06/01/2005 08:52:25 MDT Print View

I've also been following this since I'm looking for the warmest possible pad for my wife who is definitely a cold sleeper.

Very interesting, but I didn't understand this statement:
'When you lay directly on reflective Mylar there isn’t a sufficient air gap to reflect the long-wave IR.'

Thanks,
B


(Anonymous)
big agnes on 07/16/2005 19:48:31 MDT Print View

From a cold sleeping, comfort seeking woman's point of view, there are two issues here. One is comfort and support, which is beautifully handled by the Big Agnes (the most comfortable air mattress on which I have slept) and insulation from cold, which the Thermarest Prolite3-Womens mattress provides. The combination is unbeatable, but not for lightweight backpacking. Your wife needs to determine whether she values comfort over cold.