Methods, systems, and apparatus, including computer program products, for determining energy indicator values for a plurality of thermoplastic materials. An energy indicator value represents expected energy requirements for performing an injection of the material in a mold cavity. An injection of each of a plurality of thermoplastic materials in a first modeled mold cavity is simulated. A respective value of a first expected energy parameter is determined for each of the plurality of thermoplastic materials based on the simulated injection of the respective thermoplastic material in the first modeled mold cavity. A respective energy indicator is determined, for each of the plurality of thermoplastic materials, based at least on the corresponding value of the first expected energy parameter. The respective energy indicator value of one or more of the plurality of thermoplastic materials is presented. In some implementations, injection of each of the plurality of thermoplastic materials is simulated in one or more other modeled mold cavity, each of the modeled mold cavities having different geometric dimensions. The respective energy indicator value can also be determined based on the simulated injection of the respective thermoplastic material in the one or more other modeled mold cavity.