Space Blanket UQ

[AaronAlso]

If you're using the space-blanket, check out Insul-Brite... It's $6/yd, and pretty warm... but easy to find...

Now that is interesting stuff there. $4.25/yd@45" on amazon.

I was thinking Thermoflect (what the AMK bivy is made from) instead, but the raw fabric is not sold comercially. You can buy it as 48"x84" blankets though.

[DaleW]

A couple of notes. If you use the space blanket on both sides, the fill has no function as your body heat is being reflected by the inner space blanket, right? If you use a less full batting and a breathable inner layer, you may be able to compress it smaller. You would also notice an increased amount of insulation if you snugged the ends a little better leaving the center more loose. Excellent beginning on and awesome idea though. This is a project I've been running through my gray matter as well. I think yours is better for compressibility. Mine may only have the benefit of greater durability. It merely involves an outer shell some heavy nylon.

The fill prevents convection air currents from transferring energy from the warm side the cold side. That is why there are all kinds of insulated air mattresses--- if the air can move in the space, it will move heat away from your body. Loft=saved warmth: the more loft you have and the harder it is for air to move, the warmer it will be. The fill needs to be some material that won't transfer heat easily, can be compressed for travel and regain the loft when deployed. Cost of the materials, difficulty of construction, durability, water resistance, and weight are compromises to deal with. There is no magic in insulation. If you see thin product claiming to be as warm as 2" of down or similar, be skeptical--- the laws of physics still count.

The reflective qualities of space blankets only work at very close distances. Other than that, you get wind and moisture blocking in a compact, light, cheap little package. Any inner layers of space blanket in a sandwich are blocking air movement, but not doing much if anything in the way of heat reflection. Just the top layer closest to your body is doing any real reflection. If you use polyester batting in a space blanket envelope, the bottom surface is blocking movement and moisture and just completing the package for a dead air space.

This stuff is okay for temps above freezing to get a quick and dirty insulation package. For colder temps, nothing will beat a good thick layer of insulation. It's all about cost, compressibility and weight for the protection provided.

[Captain Smiley]

So then by this, instead of building my sandwich of (from bottom to top) cheap nylon/SB/Polyfill/super cheap breathable fabric. I should flip the SB and the Polyfill? Does that sound about right?

[JohnSawyer]

So then by this, instead of building my sandwich of (from bottom to top) cheap nylon/SB/Polyfill/super cheap breathable fabric. I should flip the SB and the Polyfill? Does that sound about right?

There are several things going here:

Un-covered batting will leak heat. The slightest breeze or air current will reduce the heat carrying capacity. Then you think, well, put the batting on the inside of the quilt, against the hammock, and then SB on the outside...

That will work too, but the SB will trap moisture. With it sandwiched, the batting will retain less moisture, but if you're sweating, you'll wake with a wet backside...

Tradeoffs...

As-it, it's an expedient, cheap UQ.

If I were to make one like this, I'd get some cheap, light fabric and forget the SB. If you want it really warm, fleece the inside layer. of course, that means weight...

John

[Captain Smiley]

See now, that's super interesting. The camp blanket thing I'm using now is just a nylon shell with a fleece lining. Works great down to at least 50. It's what actually made me think about adding a SB. So maybe it would be better, your saying is basically I'm better off with what I have? At least until I start to do them cold weather hangs.

[DaleW]

So then by this, instead of building my sandwich of (from bottom to top) cheap nylon/SB/Polyfill/super cheap breathable fabric. I should flip the SB and the Polyfill? Does that sound about right?

If you are going to bother sewing an insulated pad or an UQ, go for a light ripstop or other light quality nylon with a water repellent finish-- the same sort of stuff you would use for a sleeping bag shell. Highly breathable fabric won't help you at all--- it's no different than if you made a jacket and you wouldn't want the wind blowing through. The space blanket thing only makes sense for quick and dirty stuff. You can certainly use a space blanket along with a polyfil insulator or UQ.

A space blanket will act as a vapor barrier, keeping your perspiration from migrating into your insulation, but vapor barriers are most effective in sub zero weather, where perspiration will actually freeze in your insulation and stay there. In those conditions moisture can continue to accumulate, adding weight and killing the loft and insulating properties.

[Captain Smiley]

Ahhh, I got it. That actually puts this whole thing to rest for me then. Thanks for the clarification. I'm actually in better shape than I thought. Or rather my sleep system is.

[Navigator]

DaleW, any update on in-the-field testing?