Space Blankets- Do You Carry One?
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Will Webster
(WillWeb) - M
Radiation on 10/16/2013 13:31:48 MDT Print View

Radiative heat transfer only occurs through a medium transparent to IR radiation. Put a space blanket between you and your quilt, and it just acts as a vapor barrier. Put it on top of the quilt and it will absorb heat from the top of the quilt by conduction and lose heat to the air by convection (just as the quilt itself would do), but it will not radiate IR to the inner surface of your shelter (or to the sky if cowboy camping). Suspend it above you and it will reflect the IR coming off your quilt back down.

Related to this: A lot of Reflectix's claims are regarded skeptically in the insulation community, but if you read their literature it plainly states that a minimum 1" air gap is required on both sides to get benefit from its reflectivity.

Will Webster
(WillWeb) - M
Link on 10/16/2013 13:41:15 MDT Print View

I was referred to this thread a while back when I asked about making an emergency shelter from space blankets:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=23685

Matt Dirksen
(NamelessWay) - MLife

Locale: Mid Atlantic
Re: Radiation on 10/16/2013 13:45:47 MDT Print View

Right on!

For many years, I've installed Reflectix in client's attics to reduce solar heat gain just under the rafters. The air gap between the rafters and roof sheathing gives us the space we need for proper IR reflectivity to occur. Thats about the extent of it's use in for homes, and installing it doesn't come close to the improvement that upgrading the attic insulation to R-49 could do, performance-wise.

But because I have so much of it left over from jobs in my basement, I LOVE using it, either under the tents to keep the kids from tearing up the tent floor, or to add a little bit of "comfort" under my Neorest. I also like how I can fold it up in my pack, offering more back comfort & support.

Matt

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: air gap on 10/16/2013 13:46:41 MDT Print View

Yes to both James and Greg. It's the combination of conduction and radiation.

All that matters is heat loss or temperature differential, doesn't matter whether it's radiation or conduction. I believe my 4 examples are correct and pretty much charcterize what you experience.

Some day I'm going to measure the combination of conduction, radiation, and convection.

Mike Schasch
(MSchasch) - F
oh yeah on 10/16/2013 21:21:30 MDT Print View

I don't know much about the science, but I do have some real life experience with a space blanket on 3 separate occasions. Twice in November in Zion, once in February in the Panamint Mountains above Death Valley. 2 of those were in technical canyons and one was on the side of a big wall. Was truly grateful to have a space blanket on all of these day trips. Even worked somewhat to cover up myself AND a buddy on the big wall. Trust me when I say you'll be happy to have it.

Samuel C. Farrington
(scfhome) - M

Locale: Chocorua NH, USA
'space blankets' on 10/16/2013 22:45:09 MDT Print View

Max,
I only carry one of these products when day snowshoeing in the mountains. If I had to call for a rescue, at least it's something, in addition to whatever insulation is on me and in the day pack.

The one I carry is an envelope Adventure Medical Kits calls an emergency bivy, (all their blankets say 'SOL' on the package, although some are very different in composition). It is a breathable, water resistant, nonwoven gray polyester with a reflective coating on the outside of the envelope with Velcro closures, and rolls up into a 8"x4" stuffsack weighing just under a half pound. It is very different from the lighter polyethylene blankets also sold with the SOL label, and by Heatsheets, and totally different from the crinkly, reflective Mylar space blankets.

I'm thinking that if on deep snow, there would be plenty of airspace between me and the ground. The polyester is much easier to handle than the polyethylene and mylar materials, and if very cold and hypothermic, handling stuff can be a major problem.

Hope I never have to use it. Hope 'SOL' doesn't mean what I think it might.

Edited by scfhome on 10/16/2013 22:46:14 MDT.