The material best suited for making a mold strongly depends on the type of mold you want to make. Because of their heat-sensitivity, our resins are not suited to make molds themselves. A common approach is to use 3D printing to create a master (positive shape) first and turn that, for instance, into a mold (negative shape). Due to their smooth surface, resins give the best result.
If you’re looking to make a mold for investment casting, take a look at TetraShell.