AM is rapid prototyping when AM makes a part, not meant as an end-use product, to verify a design fast. Rapid prototyping is one of the oldest and current applications of AM that makes both visual and functional prototypes. A visual prototype must look like its digital image, while it does not need to be as strong as a final product. For example, if it does not disintegrate on checking its appearance, it is strong. The functional prototype must be able to go through testing. For example, if the prototype of a nozzle is made to test the flow of air through it, it should have adequate properties to test. These properties are (1) strength, so it must not break due to the flow of air when it is fitted with an air source and (2) a smooth inner surface like that of a final product to test the flow.