I suggest watching this talk: Are mushrooms the new plastic? Stay away from conventional styrofoam. It's passé. read more
Putting Styrofoam in Compost. If you’ve decided to go ahead and add to compost, then any styrofoam used to aerate compost should be broken up into tiny pieces, no bigger than a pea. The amount you use should be proportionally minute with a ratio of 1 to 50 or more of compost. read more