This is how I make "plastic" for my projects.
All you need is:
-Styrofoam (expanded polystyrene)
-A towel or ironing board
-Common sense and safety
WARNING: DO NOT ATTEMPT TO THIS INSTRUCTABLE. IT INVOLVED HIGH TEMPERATURES THAT COULD CAUSE SERIOUS BURNS, PROPERTY DAMAGE, OR EVEN FIRE. THIS PROJECT MAY ALSO GENERATE HARMFUL FUMES THAT COULD CAUSE PERMANENT BRAIN DAMAGE.
I AM NOT LIABLE FOR WHAT YOU DO WITH THIS INFORMATION!
I hate disclaimers (but I hear getting sued is worse).
Step 1: Preperation
Lay down a towel or ironing board on the surface you want to work on so it doesn't get hot or burn. I recommend using an old one that you don't care about because it will probably get burned.
Plug in the iron and let it get hot. The temperature doesn't matter, but if it hotter it will melt faster. I'm not sure but when it gets hotter it probably releases more fumes.
Take your Styrofoam (I use packaging from a printer and spacers for bottles) and break it into smaller pieces (about 3"x3"x2"or about 80x80x50 mm) The size doesn't matter, but it makes it easier to melt.