I am in Sydney Australia (if that helps you).
Expanded Polystyrene (EPS) Insulation, Underfloor & Wall Insulation Suppliers and
A & C POLYSTYRENE P/L, Wetherill Park, NSW 2164
In terms of finish, latex paint makes them look much better than 2 coats of water-based paint. In terms of tests I defer to Jens' workwhich shows they are almost as reflective as wood.