While reading about the history of art deco design, I came across an article on bakelite. Essentially, it's just phenolic resin (the stuff they make router plates out of) used as a binder for a whole lot of sawdust. I've been wondering: Is it possible to use other materials - say, fiberglass resin - to achieve the same effect? It wouldn't be pretty, but such a composite material would be cheaper, lighter, and easier to work after casting than most cast plastics, and with a sufficient amount of Bondo and some paint could look pretty spiffy.
You can see the sort of thing I'm thinking of here:
You can mix nearly anything together with a casting or pouring resin - that makes your additive an "aggregate", much like the aggregates (stones & sand) in concrete. They're there very largely to fill space, to take up room.
In most cases, a honeycombed resin would be just as sound as a solid resin because the object isn't expected to be structural & of critical dimensions.
Fiberglass resin is usually just the same ol' polyester resin you use for casting, too. You can even do it with epoxy, although that's not usually very cheap to do. Nearly any two-part resin (resin & catalyst) will do just fine when mixed with aggregates.
It may be difficult to get the sawdust to mix WELL with your resin, though. It's lightweight & really wants to float. The resin may not be very eager to "wet" the sawdust without vigorous mixing.