“The most common way to produce plastic parts is the plastic injection molding process. When the process uses materials that can be heated to soften or melt, it is called thermoplastic injection molding. Most plastic parts today are made from thermoplastic materials such as nylon, and ABS. When the process uses materials that permanently solidify by a chemical reaction, it is called thermoset molding. Thermoplastic injection molding, which relies on the rapid cooling of the plastic melt in the mold, typically results in a much faster process cycle than thermoset molding. The principal thermoset materials molded by Rebling are DAP, phenolic polyester and epoxy.”
this was taken from- http://rebling.com/custom-molding/molding-processes/ to me it is relevant because want to cast the plaster last I have carved and use some of the materials mentioned such as Nylon and phenolic polyester to fill the cast. the reason I want to do this is so that I have a functional last that can be used to make the upper if a trainer.