The Aussies discussed a number of reflective materials, including metal-laden paints.
However, they generally came to their senses, and often came back to aluminum foil.
The guy in Cuba, clad his in some sort of very thin aluminum plate left over from commercial printing.
It was thin like the baking sheets you use to make cookies in the oven, but several feet square.
One fellow made his structure from cardboard, instead of wood.
Ya gotta watch out for those rain-showers, though.