Nature abhors a vacuum, much like my ex-wife. . . :-)

the foam would collapse as soon as it reaches ambient pressuremany materials can withstand the vacuum of space, provided they are thick enough

I would settle for a lighter than air gas foam preferably non flammable.

spray foam doesn't work because one of the attributes of closed cell spray foam is that over time the gas seeps out of it and moisture can get is which is why the insulative performance drops over time.

But on the other hand what if instead of using lightweight materials such as carbon nano-tubes, why not repurpose the tubes, by forming them inside of a vacuum and then seal the tubes. Or make vacuum sealed "bucky balls" instead. These rigid atomic structure can never implode because of their inherent perfect structure.

And if these structure are lighter than air then you may be able to put large amounts of them into a derrigable. But I bet that they wouldn't be lighter than air in the end anyway. Just a hypothesis.

Greetings,

I imagime a vacuum chamber that is injected with multi-liquid mix of chemicals that react by expanding and hardening into a Vacuum Foam Matrix (VFM), shaped to the needed size and volume.

The Vacuum Foam Matrix will need to be strong enough to hold its shape at 15 lbs PSI (or whatever earth standard pressure is), and must have a negative buoyancy in earth normal gravity (lighter than air).

The volume in relation to the amount of negative buoyancy is the key.

Any investors want to fund my research?Gordon

I first thought about this idea when I looked into buckyball structures - if you can make buckyball spheres out of interlinked buckballs then picture this:

First, lets call the smallest level of ball (144 atoms of carbon) Level-1

The next size up, 144*144 atoms, level-2

The next size up, 144^3 atoms, level-- etc

now imagine a diamonoid structure (ie pure carbon) where the outside surface is tighlty knit level-1 balls (like pure diamond. a few layers back the foam is constructed from level-2, then level-3 etc. as you get deeper into the material, you get larger pockets of vacuum, with a higher volume:mass ratio each time, but less force to resist and load to bear as you get deeper into the object. As long as this structure is created in vacuum, we could be looking at a lighter-than-air building material with the strength close to than of diamond.