Styrofoam is a very flexible material, but when you try to saw or cut with a regular knife, it can shatter and drop many balls.
Always use your own Styrofoam Cutting Tool.
There are two types of styrofoam cutter: the electric cutter and the stack cutter, both are found at stationers and craft stores.
Cutting electric part (homemade tool)
A simpler way to cut styrofoam is by heating a knife, preferably a wooden handle, to avoid heat in the hand.
You put the cutting part of the knife in a flame, it can be on the stove, and then slide the blade on the styrofoam, cut everything right.
But avoid breathing the smoke that comes out of the cut!
An excellent tip from the Hobbys site:
I use Nickel Chromium wire of 0.8mm. Thinner wire tends to burn mold, forming teeth. Thicker does not stretch properly. There are people who use simple steel wire, which is used for VCC (single wire, not braided).
To control the electrical voltage on the wire, I use a dimmer connected directly to the wall outlet. Two alligator type guitars connect the wire to the dimmer. Gradually the tension in the dimmer is increased, until the wire begins to cut the styrofoam. Do not overheat so as not to "eat" Styrofoam beyond what is necessary.
Make markings on the dimmer to calibrate it for the next cuts. The practice, in this case, is the great ally. Remember to isolate yourself from the wire, to avoid taking shock and also to avoid by fire in the shack. The maximum danger is to burst the wire (if it passes the point, then you will notice the red color and the smoke in the said saying).
Obs. Beware of tools that use electricity, can cause shocks, create a short circuit or even burn.
Seek help from an electrician before testing any home-made power tool!
Styrofoam Cutting Machine
Video: Application of polyurethane resin in styrofoam [/ h2]
Protect Styrofoam against any aggressive material by passing PVA glue (diluted) throughout. This also prevents crumbling!