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Space Blankets- Do You Carry One?
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jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: Re: Re: Re: Yep on 10/10/2013 22:12:32 MDT Print View

clothes don't create air space. As soon as IR hits the surface of the clothing it gets absorbed. You need an air space that consists of air.

A blizard suit has several layers of reflective material, then they're accordianed up using elastic. So you have reflective material, air, reflective material, etc.

A neo air mattress has internal reflective layers inside, suspended so there's air space between.

In the ceiling of a house, you can suspend the reflective material between joists so there's air space

just Justin Whitson
(ArcturusBear)
Re: Re: Re: Re: Re: Re: Re: Re: Re: Yep on 10/10/2013 22:50:37 MDT Print View

Got you, got you before too, but i guess i wasn't explaining myself well. In any case, what i was saying wouldn't really be practical anyways.

Probably also not practical; I guess one could put guy outs on a S.B. (one of the stronger SOL ones) and raise it up an inch or so from your body, but what a pain in the butt.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Yep on 10/10/2013 23:18:49 MDT Print View

My great idea is to make a tent out of reflective material

Theoretically this should work

just Justin Whitson
(ArcturusBear)
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Yep on 10/10/2013 23:24:48 MDT Print View

Sounds interesting, i'm guessing there's no current suitable material?

Funny enough, i have been thinking of making a reflective liner for my Tipi tent, but i don't know how to do it with the stove being set up inside same. I don't think putting it any where near the pipe would be a good idea.

But maybe i can just sort of hang some from the top sides and reflect it down. Probably don't really need it to begin with the stove in there. Get's plenty hot, but more interested in conserving the heat a little longer.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Yep on 10/10/2013 23:51:01 MDT Print View

The outside of a clothed or sleeping bagged body is only slightly warmer than ambient so heat loss from radiant heat loss is small - what did someone say, 20% of total heat loss?

A stove is hot. Radiant heat reflected would be a lot more.

You can buy space blankets.

Go to a store that sells stuff for growing (marijuana) plants indoors. They sell reflective material.

just Justin Whitson
(ArcturusBear)
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Yep on 10/11/2013 00:00:56 MDT Print View

Just got a bunch of the SOL emergency ones, a couple double sized ones and couple single sized ones. Have had and used some of the mylar space blankets, but like the SOL ones more so far. It's polyethylene instead.

Thank you for the info. If you ever build that tent, let us know.

eric chan
(bearbreeder) - F
VBL on 10/11/2013 00:04:07 MDT Print View

one thing that is useful when its not cold enough for a full fledged VBL ... but when you may want the occasional boost in cold nights ...

is to wrap oneself in one of the more durable emergency blankets, or one of those 4 oz bivies ... it provides a decent heat boost

of course you have to remember to put your puffy between the the blanket and the bag rather than wear it or itll get damp ... of if you wear the puffy, wrap it around your torso under yr puffy as best you can

;)

Jason Elsworth
(jephoto) - M

Locale: New Zealand
Space Blankets- Do You Carry One? on 10/11/2013 02:23:59 MDT Print View

If you wear the puffy, wrap it around your torso under yr puffy as best you can.

I did that with a small cuben groundsheet one night when I was stuck out without a sleeping mat. It worked well.

Jennifer Mitol
(Jenmitol) - M

Locale: In my dreams....
Re: Space Blankets- Do You Carry One? on 10/11/2013 08:17:20 MDT Print View

Do they really use them in space?

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Space Blankets- Do You Carry One? on 10/11/2013 08:24:23 MDT Print View

yeah, they use them on satelites to control temperature

there's no air, so no conduction, so all you have is radiation

either absorbing heat from the sun or radiating it to space

Dale Wambaugh
(dwambaugh) - MLife

Locale: Pacific Northwest
Re: Space Blankets- Do You Carry One? on 10/11/2013 11:02:26 MDT Print View

Space blankets are a "better than nothing at all" option for emergency use. IMHO, it goes in the "extra clothing" slot in the list of hiking essentials. I carry one of the bivy sack style AMK blankets for day hiking emergency shelter an long with my poncho.

What you get is an inexpensive, light and compact sheet of material that is windproof and waterproof. You can simply wrap it around yourself and sit under a tree if you are too messed up for better options. They make a good ground sheet and can be used to waterproof the roof of an improvised shelter. You can rig one as a windbreak an reflector in front of a fire.

A night spent with a space blanket might be miserable, but it can give you the edge to survive to complain about it :)

If you have your full multi-day kit, it is redundant. It may have more use as a first aid item with a group.

Some folk use them as their regular ground sheel. The Mylar ones are noisy and prone to tearing. The AMK versions are polyethylene and quieter and tougher.

Dean F.
(acrosome) - MLife

Locale: Back in the Front Range
Not for hiking on 10/11/2013 12:33:50 MDT Print View

I don't see much point in carrying a space blanket while hiking/camping, for the myriad reasons already listed. However, I do keep one in my "man-purse"- the little satchel I carry sometimes on short jaunts. It's my non-UL daily survival bag: a nalgene nested in a titanium mug, a knife, a firestarter, a windshirt, some snacks... and both a polycro groundsheet and a space blanket still in the wrappers so that they are small.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Re: Space Blankets- Do You Carry One? on 10/11/2013 12:48:29 MDT Print View

"Do they really use them in space?"

The Hubble Space Telescope does -

Hubble

marc D
(mareco) - M

Locale: Scotland
Space Blankets- Do You Carry One? on 10/11/2013 12:55:45 MDT Print View

I always carry one, though fortunately never had to use them. I have given a couple to people who have got into difficulties in the mountains and were needing picked up by the mountain rescue teams, it seemed to make a difference to them.

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Space Blankets- Do You Carry One? on 10/14/2013 21:19:26 MDT Print View

I carried one for decades. Never used it. So I removed it from my pack along with most of my first aid kit.

Greg F
(GregF) - F

Locale: Canadian Rockies
air gap on 10/15/2013 18:35:57 MDT Print View

The air gap does not affect radiative heat loss as air essentially has an emissivity of 0 and the emissivity of a material is determined by surface finish and what it is.

Air Gaps will generally decrease conduction as air is not very thermally conductive and if you restrict the air flow you will reduce convection. However it does not have an affect on radiative heat loss.

just Justin Whitson
(ArcturusBear)
Re: air gap on 10/15/2013 19:14:21 MDT Print View

Translation for us non physics, engineer, etc. types?

Are you saying that a space blanket will still work if more directly on the body with very little air gaps between your body and the S.B.?

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: air gap on 10/15/2013 20:28:01 MDT Print View

#1 - If you have body, clothing, space blanket, clothing, air - space blanket does very little

#2 - Body, clothing, space blanket, air - space blanket reduces maybe 20% of your heat loss

#3 - Body, clothing, air space (I don't know how you'de accomplish this), space blanket, air - the space blanket might reduce your heat loss 40%

#4 - body, clothing, blizzard survival suit that has several layers of air and space blanket - that would provide some real warmth, might be a good alternative to a sleeping bag

This is my opinion based on theory, measurements, looking on the internets but may be contoversial?

Greg F
(GregF) - F

Locale: Canadian Rockies
Re: Re: air gap on 10/16/2013 12:53:42 MDT Print View

I will try to explain it a little better. I was on my phone so I was farly brief.

There are 3 methods of heat transfer
- Convection - heated air moving and escaping and being replaced with cold air. A drafty window which leaks around the edge is letting heat escape through convection
- Conduction - Heat that is transferred through the medium. If you put your hand on the window glass it will be cold and your hand will become cold because the glass conducts heat into your hand.
- Radiation - Electromagnetic waves are emitted from virtually everything. These waves contain energy and as such emit heat. They are governed by equation q = esT^4A where q is the heat loss, e is the emissivity, s is a constant A is the area and T is the temperature. So looking at the equatuion the only way to increase or decrease the rate of radiation is to change the temperature of the material, the surface area, or the emissivity. If you notice in the equation that an Air Gap or thickness is not a factor. Therefore radiation is not affected my the gap.

This means in terms of radiation is does not matter where the reflective layer is. Also to determine the effectiveness of the space blacket layer vs say a layer of nylon you would just compare their emissivity.

Now this does mean what Jerry is expericing or measuring is incorrect. Its just not do to radiation. Conduction the equation is essentialy a function of thickness, and heat loss due to convection can be reduced by limiting air movement by creating multiple pockets of air that can't flow into each other.

I would suggest that what Jerry is observing is that the air gap decreases conduction and therefore is warmer.

James Klein
(jnklein21) - M

Locale: Southeast
air gap on 10/16/2013 13:12:27 MDT Print View

With no air gap (or just 'space') between emitting surface's, there will be no meaningful temperature differential and therefore no meaningful IR exchange to block.