The mass or heft of a print can be important. Most plastics will feel very light in the hand, which may not provide the tactile feedback needed for the person.
3D- PT recently received samples of eSUN PLA and Bronze PLA to test.
The bronze filament felt great, and looked like bronze wire on the spool. This is a far cry from the muddy brown of Colorfabb BronzeFill. It also had some serious heft compared to other composite filaments. Brass filament printed great, and when you print it into a filament, it adds some more mass and density to an otherwise lightweight print.