space blanket question

[hollowdweller]

assuming you were sleeping inside a sleeping bag on a trail pad and inside a sleeping bag cover/bivy and you were going to use a space blanket too: Would it be best to put it on top of your bag, since the heat rises and the ground would be somewhat insulative(sp?) or underneath your bag?

 

[Neal]

Actually heat itself is non directional. If it heats air then the heated air will rise which is a form of convection.

A space blanket reflects radiation which would be different than convection or conduction of heat. Would be like on a cold night when the camp fire is down wind of you but you still feel the heat because radiated heat travels like light and only produces heat when it hits a solid object.

If the space blanket is touching your skin, it will have no more effect than any other plastic bag. There needs to be a space between the space blanket and your skin. Cloth is enough space.

The more area around your body the space blanket covers, the more radiation it will reflect back to your body. It can only reflect a percentage of what your body gives off in radiation. Besides reflecting radiation it also is a layer of insulation, as much as any plastic sheet would be of equal thickness and also a wind barrier.

It is also a moisture barrier, which can be a problem in a sleeping bag.

Neal

 

[Robert H]

There is a common trick to put a space blanket inside a poncho liner to get a little more insulation. A little noisy, but the weight ration pays off.

 

[StuU]

I spent a *very* cold night back when I was a teenager. The idea was to test out the space blanket on an autumn camping trip in the Appalachians. I ended up sleeping on a car seat wrapped with the space blanket. Never have I appreciated the morning sun so intensely as after that chilly night.

 

[Moine]

Space blankets work fine as heat reflectors... For example, if you have a fire, put the blanket behind you (assuming you face the fire). It will reflect the fire heat.

For short term "reheating", sit down and wrap yourself in the blanket. Then light a candle or a lighter inside the blanket. It will heat up pretty fast and heat you nicely.

A drawback of those blankets is that they are totally waterproof. Not breathable at all. If you wrap them too close around you (say inside your sleeping bag instead of outside), they'll condense water from your perspiration and make you wet... And being wet is definitely NOT GOOD when it's cold.

Cheers,

David