A question about air inflated insulation and hammocks

[Dale Wambaugh]

I get the process with uninsulated air mattresses transferring heat due to convection currents when used on the ground, but I'm hoping that hammocks may be a little different. You can start by throwing out the need to support the user's weight and actually pressing down on the mattress surface.

What would happen if you took a big space blanket envelope and filled it with long balloons and put that between the hammock bottom and an outer cover of silnylon? You would have two reflective space blanket surfaces separated by 4" or so of air in a balloon, with a layer of breathable nylon above and a non-breathable layer below, topped off with a compressed sleeping bag layer and a 98.6F heat source.

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[Ken Thompson]

An underquilt would probably be lighter.

[Dale Wambaugh]

A space blanket is 3oz and a few balloons? It's the physics I'm after!

[Keith Selbo]

If you throw in some leaves or pine needles to break up the air flow, I think your setup would work pretty well.

[Dale Wambaugh]

There are lots of alternatives. I have experimented with crumpled and folded space blankets inside another space blanket made into a bag by folding and taping three sides. That is practical to carry and cheap to make. I tried a space blanket quilt with cheap polyester fill inside too.

The thing I am after is the difference between laying on an insulating layer on the ground vs being in minimal contact with insulating material while suspended in the air. I understand the issues with convection in an uninsulated air mattress on the ground, but what happens when you aren't pressing down on it and you have the reflective materials added to it?

You end up with a sandwich– this is under the hammock surface, with no consideration to clothing or compressed sleeping bag layers and the like:

hhhhhhhhhhhhhh hammock fabric (breathable nylon)
aaaaaaaaaaaaaa air space
ssssssssssssss space blanket
aaaaaaaaaaaaaa air space
{{{{{{{{}}}}}} alternative layers (more space blankets and or layers or poly fill)
ssssssssssssss space blanket
aaaaaaaaaaaaaa air space
oooooooooooooo outer cover (silnylon in my prototype)

[Paul Ashton]

Although the "matress" is not in contact with the ground, it is in direct contact with the air surrounding the hammock. Any movement of that air (ie draught) will extract heat by convection. To reduce that, the air pockets within the "mattress" need to be broken up to very small pockets by filling with down or batting to prevent the air from circulating within the matress, allowing convection and heat loss. Down is lighter and more compressible, but much more expensive. peole have used windshield sun reflectors as insuation as the refective surfaces are kept apart by bubble wrap type material, which keeps the reflective surfaces apart, allowing them to work, while breaking the "air space" to be broken down to lots of small bubbles to reduce convection losses. Easy to make from a roll of refletix.

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