There are several companies who create miniatures out of polystyrene. The material is also called soft plastic among the modellers. I've collected the sources and tutorials I've found interesting.
Handling polystyrene miniatures
Zirrian: How to work with soft plastic - a tutorial (in Hungarian): A good article about handling polystyrene.
* * *
Do you know other ways to handle polystyrene miniatures? Do you know other good resources? Tell us in the comments!