Interior walls

[randomq]

With the weather getting hotter and the possibility of more bad air days, we've considered insulating, double-walling, and shuttering a room in our house (currently just openings with screens as terracore described). I wonder if that radiant barrier is enough to make air-conditioning efficient, or if we will need actual insulation as well? What do people in Hilo do with their single-wall homes when the temperature outside is 90F+?