Making a negative to mold plastic?

Question:I was wondering if anyone knew of a good, yet inexpensive material that would be good in making a negative for a mold and to pour liquid plastic into and remove without damaging it. It would also have to be fairly large, say about 6 ft by 6 ft.

Best Answer - Chosen by Asker: I was wondering if anyone knew of a good, yet inexpensive material that would be good in making a negative for a mold and to pour liquid plastic into and remove without damaging it. It would also have to be fairly large, say about 6 ft by 6 ft.

I used plaster of paris to mold masks of faces and other body parts. But that large is going to be expensive no matter what you use.