I want to cut an 8" round styro in half - what tool will give me the cleanest cut? Will a regular (long) knife work?

Craft stores, such as Michaels, sell an inexpensive cutter just for styrofoam. I tried with a knife, and a lot of "crumbs"

The cleanest cut you'll get is from a "Hot Knife" you can find the at most craft stores for about 15-20.00 They are easy to use and you'll eliminate the mess.

Hot knife is the way to go. It is basically a heated wire used to cut through. A blade is going to give you a messy cut.

I have a hot knife that I cut 1/2" thick foam coard board with - is that what you're talking about? How will I be able to cut through an 8" dummy with that?

Thanks!

you can use a electric knive

I just watched Ultimate Cake Off and a guy on there just heated a frosting spatula with flame and used that. The judges were impressed, lol. I'd try that before I spent unnecessary $ on something fancy.

Cutting styrofoam is easy, just heat a knife on the burner of a stove and that's it.  I've bought those hot knives at the craft stores and they break all the time.  this is the easiest method.  

I used an electric knife