3D printing is the process of generating three-dimensional (3D) solid items. 3D printing creates an object layer by layer. Typically, 3D printers use plastic because it is easier to use and less expensive. Some 3D printers can 3D print with additional materials, such as metals and ceramics, although they are prohibitively expensive for most individuals. 3D printers are useful because they can create new products quickly and with great detail. This means that an engineer can test many novel concepts without having to wait for someone else to create them. They are also handy for repairing plastic parts and manufacturing toys, figures, and models.