We Got Lots of Great Ideas From the Space Program; Insulation Isn't One of Them

Public Domain. NASA photo used in Tang ad

"Radiative barriers" may work well in space, but not so well down here.

There are many things that NASA and the American space program have given us. Tang is not one of them; space blankets are. Writing in Passive House + magazine, Toby Cambray of Greengauge Building Energy Consultants explains that they are radiative barriers that work really well in space as insulation but not so well down here on earth.

Lots of space insulation, like ceramic paint and radiative barriers like foil-faced bubble wrap, are sold on earth. I have used it myself in a cabin. Years ago, Martin Holladay wrote about how the stuff is good for Halloween costumes but should never be used for insulation, and Allison Bailes called it a sham. But I have never really seen a clear explanation of why something like this works in space but not on Earth until Cambray's article, What can space travel tell us about building science? I have posted portions of here with permission from Passivehouse +. (Subscribe here for print and online version to read the rest)

space blankets on Viking

Viking Satellite Thermal Blankets/ Lennart Noring in Wikipedia/CC BY 2.0

If you think back to classroom physics, heat can move via convection, conduction and radiation. As counterintuitive as it might seem, in space, objects don’t lose heat via convection or conduction, because there isn’t any matter adjacent to them. Radiation on the other hand is a big deal, you’re either losing huge amounts to deep space, or gaining huge amounts of solar gain.
Radiative heat loss or gain in terrestrial situations is mostly down to the net difference in radiation between two objects. Any object above absolute zero will emit some radiation, so if you have a cup of room temperature water next to a hot cup of tea, they both radiate heat to each other, but the hot one radiates more, so the net effect is for the hot cup to radiate heat to the cold one. In space there’s mostly no objects to exchange radiation with, so it just flies away forever, and your radiative heat losses aren’t offset by gains from nearby objects at a similar temperature, as they are on Earth.
To solve this problem, NASA invented metalised plastic films to create a radiative barrier, and hence the ‘space blankets’ commonly distributed at mass sporting events or disaster relief situations. This technology has also been deployed with debateable efficacy in the construction industry in the form of multi-foil insulation. Unfortunately, while this works really well in a vacuum, in the presence of air convection and conduction come back into play, and the most practical solution to that is a good thickness of something fluffy.

So that's why we use fluffy stuff on Earth and radiant barriers in space. Now it's time for some Tang.