I actually believe the difference is that one is suitable for moisture more so than the other, as it is meant to be used outside of a house for insulation.
we use electric turkey carvers for shaping foam ;-p
i know i'm way late on this discussion, but you can make a foam construction a lot more durible by painting it with foamcoat (you can even do cool tints with that stuff, its rules!)
oh and i'm positive, the difference between pink and blue foam is just the color
we've used foam for alot of stuff, we used to make pairpets(sp?) for once upon a mattress. we also used it to make column things for the mikado. we call the stuff stibbe stone after one of our techies.