Is black foam a good insulator?

Polystyrene foam is a good insulator.

The characteristics that make polystyrene is a good insulator stems from its composition of long polymer chains and because it encapsulates regions of gas in the form of a closed cell foam. Air and gas in general are poor conductors of hear when convection is inhibited as it is in a foam. (The form used in insulation is often a closed cell foam, but that is not the only form taken by polystyrene.)