i know that you use foam to create a model and when metal is poured on top of it it evaporates on contact but what about if you tried it with regular common plastic models and put a runner and riser hole for the plastic to vent similar to sand casting
Any organic material can be used to make a casting mold including twigs, other wood and plastics, as long as it is burned out before the metal solidifies. The problem with using anything other than foam is that foam is mostly air that is surrounded by a small amount of plastic. When the plastic is hit by the hot metal, it burns/gases off without cooling the metal enough to block its flow. For any solid organic material, the investment must be fired/baked to a high enough temperature to turn the material to ash which can be blown into the vents by the flowing metal.
