For example, a final product that will be made by plastic injection molding will require expensive custom tooling, so a prototype for this product may be fabricated by machining or stereolithography instead. Process: Mass-production processes are often unsuitable for making a small number of parts, so prototypes may be made using different fabrication processes than the final product.
In some cases, the final production materials may still be undergoing development themselves and not yet available for use in a prototype.
Such prototypes are commonly used for early testing of a software design, and can be part of a software walkthrough to confirm design decisions before more costly levels of design effort are expended.