FFF or Fused Filament Fabrication printing, also known by FDM or Fused Deposition Modeling (a term trademarked by Stratysys, Inc.), is a printing method that heats a solid thermoplastic filament to a semi-liquid state and extrudes it in thin layers, one upon the other. Once the material cools, the part becomes solid. This is a very common type of 3D printing. Parts printed using this process are brittle and not sustainable for mechanical parts. Being that parts are printed in layers, they are weaker in one direction than the other.

SLA or Stereolithography printing uses vat polymerization. A photo-polymer resin in a vat is selectively cured by a light source. Unlike FFF printing, this method produces a smooth finish with fine detail. Like FFF printing, this process also creates brittle parts that are not suitable for mechanical parts.

SLS or Selective Laser Sintering uses powder bed fusion. A bed full of powdered plastic provides the material to build parts. A laser is used to heat the desired areas, fusing the plastic powder together to create the desired part. The bed drops after each layer, the powder is distributed evenly, and the process is repeated until the final dimensions have been reached. A similar process can be used to fuse metal powder into usable parts. This process is known as DMLS or Direct Metal Laser Sintering.

Exotic filaments (sometimes seen as hybrid filaments) are becoming more popular and the range is widening. Some of these include wood, metal, and clay, which all contain a powder or fiber mixed with the polymer to produce a unique look. Since these filaments contain other materials, they behave differently, as well. Other exotic filaments look normal but have altered properties. They can be magnetic, conductive, glow-in-the-dark, color changing, or flexible. Some even dissolve in water!

Flexible filaments generally consist of TPC (thermoplastic copolyester), TPE (thermoplastic elastomer) and TPU (thermoplastic polyurethane). These materials are much like a printable rubber. The difference between the two lies in their hardness values. Nylon filament is also gaining in popularity.

Rigid filaments are the typical, everyday filaments. The most prevalent are ABS (Acrylonitrile Butadiene Styrene) and PLA (polylactic acid), but there are a variety of others. Some other significant rigid filaments include PETG (glycol-modified polyethylene terephthalate), PC (polycarbonate), ASA (acrylonitrile styrene acrelate), POM (acetal), and PMMA (polymethyl methacrylate).

PLA is the most popular filament. It is easy to print with, has a lower printing temperature than ABS, doesn't warp easily, does not produce intense fumes when printing, is biodegradable, and can be food-safe (check the manufacturers specifications). It is more environmentally friendly than many other filaments as it is made from renewable resources like corn starch and sugar cane. The main issue with PLA is that it is brittle. Avoid using it when making items that might be bent, twisted, or dropped repeatedly.

ABS is the second most common filament. It is slightly more difficult to print with than PLA, as it has a tendency to warp during cooling. ABS is tough and able to withstand high stress and temperature and it is moderately flexible. It does, however, emit very strong fumes when printing. ABS is used for many household and consumer goods, like LEGO's and bicycle helmets. An important thing to keep in mind, though, is that 3D printed parts are significantly weaker (70% or more) than their injection molded counterparts.

Soluble filaments include HIPS (high impact polystyrene) and PVA (polyvinyl acid). These materials can be used as support materials and later dissolved away to create parts that would otherwise be or impossible to print. HIPS can be dissolved in limolene, where PVA can be dissolved in water.