Reply To: Interior fill for 3d prints

I think your best is to look at the polyurethane casting resins we were considering back in this thread:

Casting Epoxy for Phone Cases

and if you want weight, to mix up a slurry with some kind of metal powder, like tungsten powder (http://www.amazon.com/Dynacraft-Tungsten-Powder-Jar-8-Ounce/dp/B00LU0W5CA heavy but expensive) or stainless steel powder (http://www.amazon.com/Stainless-Steel-Powder-325-mesh-1-lb/dp/B017Y2HOQO somewhat cheaper) or iron filings (http://www.amazon.com/Iron-Filings-1-Pound-Package/dp/B008MB17GA/ much cheaper)

Metal filled resins are very common for “cold casting” like described at http://www.castingabout.co.uk/Cold_Metal.html, and high fill rates like 2:1 metal:resin by volume have been documented, although if I were you I would probably add metal incrementally.