[zdragnar]

The less rain you get (i.e. during a drought) the more you tend to get dust in the air. We went through this last summer; my dog would kick up clouds of dirt dust running through our yard.

Worse than this, though, is the durability of the material. Lots of these super reflective paints don't hold up very well to rainwater (which itself is not especially clean or PH neutral) or seasonal extremes.

Typically, you wouldn't want to paint the sides of buildings, as that'll just reflect the light mostly down. You want it on rooftops, which most people don't pay to clean frequently or at all.

[kulahan]

This makes sense; I guess it just becomes a new added expense with no major benefit aside from maybe saving on some cooling costs? Seems like a thing you'd be able to convince a company to buy into completely, but only once it's cheap and durable.