Prototype Casting

Hi;
I need to cast parts of a prototype in a plastic similar to that of
Tupperware or something like that. Problem is that I know nothing about what
this type of plastic is called or where to get it. The main properties that
I'm looking for is the ability for the plastic to be bent and abused and
still keep it's basic shape. Heat resistance and being able to microwave are
irrelevant.
Does anyone know where to get someting like this?
Thanks
Lars