A machine (often called a replicator) builds solid models using a PLA or an ABS plastic filament one layer at a time. Each layer thickness is roughly 1/16". This service can create prototype parts for basic testing and fitment purposes, and depending on the application, these models may or may not be able to be used as final products. 3D printing is a cost-effective, additive process -- you only pay for the materials used and there should be no scrap generated.