I'm wanting to get into casting and I have done some so far but I've found a problem, what medium. I've tried two of them, straight Plaster of Paris and Tough Stuff Large Gap Filler. The Plaster of Paris while strong was heavy, two pounds at the heaviest casting. The Tough Stuff turned out lighter, but I have no idea how it filled my mold (a make-shift mold/trash item from work) since I could not get the foam out of there. To get to the point of this, I was wondering if anyone knows of a strong but light casting medium that'd work for casting in Hirst Arts molds and others.