I'm looking for a cheap material that I can fill plastic hollow model's with, that will harden up, to give the model a good weight. The model's are being made by a 3D Printer, and if made hollow, they don't weight a whole lot. Any suggestions?
That would depend to a large extent upon what you intend to do with the model. If it's going to sit on a shelf for display, I'd just fill it with sand since there'd be no need for something solid inside. Other than that, the purpose would determine what sort of weight you want. The choice of material should be based upon specific gravity rather than general physical properties. Cement will do the same job as silicone, but it will be a lot heavier. There's also a whole field of binary materials such as automotive body filler, acrylic "paperweight" liquid, Jell-O (think Gummy Worm concentrations), JB Weld, etc..
What do you want the end result to be?
Basically just have heavier model's, a lot of the time they will just be sitting up on a shelf, but I do move them around and people like to pick them up and look around at it. Sand would be a OK option maybe if completely filled with it, as to not have a "shaking" sound inside the model. I was thinking maybe even some BB's mixed in with elmer's glue, I'm just not sure how well I will be able to squeeze the glue into the models. Cement would probably be ideal for what I'm after, but maybe a bit too messy/much to work with than what I was looking for, I'm not sure though. By the way, thanks for the reply's
Actually, your BB idea is a good one, and not at all hard to implement. There's no need to "squeeze the glue into the models". Just roll the BB's in a puddle of glue and toss them in. They'll stick to each other inside and the glue will dry.