I have bought a blue styrofoam which is too thick to use, and I wanna cut it in half, I tried to use a saw and knife but no good result at all, could anyone suggest any particular tool for cutting styrofoam? Thank you!

I think the best tool for that would be a hot wire styrofoam cutter.

After that, a bread knife.

If you have a soldering iron it will make a decent job as well, specially if you attach an old blade to the tip with wire

Thx all! I will try both styrofoam cutter and bread knife too see if they work.