What is 3D Printing?
So, what is 3D printing and types of materials are printed? 3D printing is a manufacturing technique invented in the 1980s used to create 3D objects. This type of manufacturing is called Additive Manufacturing (AM). A 3D printer creates the desired object by adding layers of material on top of each other. This occurs by applying material onto a print bed based on instructions defined by a 3D CAD file, most commonly in STL format. 
There are many types of 3D printing technologies available or in early stages of development. (See article on 3D technology processes). The most common 3D printers available today use filament, resin, or powder material.
Three main categories of 3D printing technologies:
Filament – Material Extrusion most commonly known as Fused Deposition Modeling (FDM). Much like a hot-glue gun, but with plastic material. Filament, rolled up in a spool of thermoplastic material, is applied layer-by-layer thru a heated nozzle onto the platform of the 3D printer. Each layer can be as thin as .05mm or 50 microns. This thin layer solidifies quickly, creating a three-dimensional object as layers are added.
Resin – VAT Photopolymerization most commonly known as Stereolithography (SLA). Similar to dipping your hands in a pool of melted wax at your local carnival to create a hand sculpture. Liquid resin is used to form a solid object. Except that the liquid is cured, or hardened, by light. This process is called photopolymerization. A laser, or UV light, projects into the container of liquid to harden the material. Depending on the 3D printer this is done point-by-point or as an entire layer at one time.
Powder – Powder Bed Fusion most commonly known as Selective Laser Sintering (SLS). A laser sinters, or melts powdery material based on a cross section plain of a CAD model. This process repeats binding material one layer at a time until the model is complete.
Materials used to make 3D printed objects use a variety of polymer composites. (Check out my guide for 3D printing materials.) Whether in filament, resin, or powder form, a variety of materials are available to create different forms of rigid or flexible parts.
3D printers are becoming more available and cheaper thus becoming more popular to the general public. Hobbyists are using 3D printers for creating miniatures, cosplay items and household objects. But one of the most common uses for 3D printing in the manufacturing world is rapid prototyping and the tooling needed to make them.
Aside from the 3D printing technologies mentioned above others include Material and Binder Jetting, Direct Energy Deposition, and Sheet Lamination. Modern industrial-grade 3D printing systems are being used for practical applications. Some examples such as dentures, prosthesis, automotive and aircraft parts.
3D printing technologies has even ventured into the printing of food, such as with any type of food paste. Pancake batter, cookies and frosting, cakes, and even pizza are some examples. Homes are being built, or printed, out of concrete using large robot arms.
Check out our list of best overall filament 3D printers or our list of best resin printers available today.