What manufacturing process involves stacking layers of material in order to create a finished part?

Additive manufacturing is the correct answer because it specifically refers to processes where material is layered to create an object. This technique involves adding material, often in the form of plastic, metal, or resin, in a precise manner to build up a three-dimensional part from a digital model. Common technologies within additive manufacturing include 3D printing methods like fused deposition modeling (FDM) and selective laser sintering (SLS).

In contrast, subtractive manufacturing involves removing material from a solid block, which is fundamentally different from layering material. Thermal manufacturing might involve processes like welding or forging, which do not inherently layer materials but alter their state or shape through heat. Comparative manufacturing is not a recognized category in the context of manufacturing processes, making it unrelated to the question. Thus, the defining characteristic of additive manufacturing—building objects layer by layer—sets it apart and validates it as the correct choice.