Space Blankets- Do You Carry One?

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.

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

;)

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.

Do they really use them in space?

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

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.

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.

"Do they really use them in space?"

The Hubble Space Telescope does –

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.

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

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.

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.?

#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?

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.

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.

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.

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

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

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.

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.

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.