|Smite Makes Right|
I can't speak for Ninja Division, but at reaper miniatures, except for the CAV line (vehicle/mech line), the miniatures are sculpted by hand primarily in epoxy resin. CAV miniatures have 3D printed masters to make the normal casting molds. There may be be specific exceptions in the case within a line.
Different companies will have different practices. For example, Privateer Press has streampunk mecha miniatures and sculpts them by hand. Rackham's Confrontation line is sculpted using Sculpey (which contributes to the very fluid sculpts) as opposed to the more common Kneadatite or milliputt.
"white-metal" amalgam of tin, aluminum and other trace metals
Polyethylene terephthalate (PET or PETE)
High-density polyethylene (HDPE)
Polyvinyl chloride (PVC)
Low-density polyethylene (LDPE)
most prominent companies use
1)spin casting; material is poured into a mold type, and centrifugal force pulls the material into the mold design
2) Rotoscoping; material is formed using a pres mold then a cutting bit or stylus is, computer assisted, to force shapes
3) 3D "resin pulled" (Official procedure name varies); similar to 3d printing, except the object is formed IN the pliable liquid material and the shape is formed an pulled out of the material. this helps create a smoother shape and avoids the typical transition lines and material breakdown typical of common 3D printing
4) Injection molding; just like it sounds, active material is injected with high pressure and temperatures into a tightly controlled mold press