I have a walk-in attic. We use it for storage. It has blown-in insulation and a wooden deck. It is vented. I would like to put 5" of poly-styrene down. Should I put down a vapor barrier first? I also thought about putting down 2" of insulation that has the radiant barrier on both sides. Does this perform as good or better than putting down 5" of the other? If it is better, do I have to worry about moisture?

Also, would you use the white, pink or blue poly-styrene? What is the difference? I have hear the pink and blue are bad for your health.