Is styrofoam food-grade?

[Joel Berg]

I am building an AP system for my Grandfather and was planning on installing a simple RAFT growbed. We are really concerned about food grade materials for this tank because we want the entire system to essentially be organic. Do we need to be concerned about whether the styrofoam insulation people generally use for a floating raft is food grade or not? Where would you recommend buying food grade styrofoam?

Thanks,

Joel