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.