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Quoting from the Wikipedia article:

A solar balloon is a balloon that gains buoyancy when the air inside is heated by the sun's radiation, usually with the help of black or dark balloon material. The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a hot air balloon.

What material would be the most efficient (minimize material mass, maximize payload, maximize heat retention) for weaving the skin of a solar hot air balloon? I want to consider thermal conductivity of the outer surface, radiance of the inner one, and structural strength. I want to achieve the 60 metric tons payload lifted to at least 200 meters over tropical sea level.

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    $\begingroup$ What details can you give us about the design of your balloon? Please read this community wiki about design questions. We would be glad to help you with your design but you have to give us more than a concept. $\endgroup$
    – Air
    Feb 22, 2015 at 22:01
  • $\begingroup$ @Air I think it is a pretty good question now with the added definition of a solar balloon. $\endgroup$
    – Chris Mueller
    Feb 23, 2015 at 13:05
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    $\begingroup$ The lack of definition for a solar balloon is not the problem with this question. Juan asks which material is most efficient, but doesn't give enough specification as to how he determines that. When you say "most efficient" and then give 3 measuring factors, you have to state how you want those weighted. Specify minimums on the outer absorptivity, inner reflectivity, or payload weight. I could select materials that keep nearly all the heat in, but take 2 days to absorb enough heat to inflate. I could argue that's efficient, but not in the way you want. $\endgroup$
    – Trevor Archibald
    Feb 23, 2015 at 17:46
  • $\begingroup$ @TrevorArchibald I think given the application, reasonable assumptions can be made about what he means by most efficient. You're example is, as you've alluded to, clearly not what he is looking for. $\endgroup$
    – Chris Mueller
    Feb 23, 2015 at 18:16
  • $\begingroup$ Yes! indeed sorry i've been away for a while... by most efficient i mean maximum payload, maximum elevation and maximum tensile strength, minimum material mass (note: i would like it tied down at all times so must account for rope weight, and tensile strength etc...) to limit the question lets say a mark of 60 metric tons net payload is desired. $\endgroup$
    – Juan Bautista
    Dec 25, 2015 at 19:29

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It is a very broad question as there are many design considerations involved, but a good place to start is looking at BoPET(mylar) because it has a high strength to weight ratio and can be made very thin.

Clear mylar on the outside, possibly reflective mylar on the north, and black mylar on the inside. There are lots of other ways to optimize once you have clearer picture of the design.

https://en.wikipedia.org/wiki/BoPET

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