Guide to 3D Printing Materials: Types, Applications, and Properties

There are dozens of plastic materials available for 3D printing, each with its unique qualities that make it best suited to specific use cases. To simplify the process of finding the material best suited for a given part or product, let’s first look at the main types of plastics and the different 3D printing processes.

There are the two main types of plastics:

• Thermoplastics are the most commonly used type of plastic. The main feature that sets them apart from thermosets is their ability to go through numerous melt and solidification cycles. Thermoplastics can be heated and formed into the desired shape. The process is reversible, as no chemical bonding takes place, which makes recycling or melting and reusing thermoplastics feasible. A common analogy for thermoplastics is butter, which can be melted, re-solidify, and melted again. With each melting cycle, the properties change slightly.

• Thermosetting plastics (also referred to as thermosets) remain in a permanent solid state after curing. Polymers in thermosetting materials cross-link during a curing process that is induced by heat, light, or suitable radiation. Thermosetting plastics decompose when heated rather than melting, and will not reform upon cooling. Recycling thermosets or returning the material back into its base ingredients is not possible. A thermosetting material is like cake batter, once baked into a cake, it cannot be melted back into batter again.

The three most established plastic 3D printing processes today are the following:

• Fused deposition modeling (FDM) 3D printers melt and extrude thermoplastic filaments, which a printer nozzle deposits layer by layer in the build area.

• Stereolithography (SLA) 3D printers use a laser to cure thermosetting liquid resins into hardened plastic in a process called photopolymerization.

• Selective laser sintering (SLS) 3D printers use a high-powered laser to fuse small particles of thermoplastic powder.

Fused deposition modeling (FDM), also known as fused filament fabrication (FFF), is the most widely used form of 3D printing at the consumer level, fueled by the emergence of hobbyist 3D printers. 

This technique is well-suited for basic proof-of-concept models, as well as quick and low-cost prototyping of simple parts, such as parts that might typically be machined.

Consumer level FDM has the lowest resolution and accuracy when compared to other plastic 3D printing processes and is not the best option for printing complex designs or parts with intricate features. Higher-quality finishes may be obtained through chemical and mechanical polishing processes. Industrial FDM 3D printers use soluble supports to mitigate some of these issues and offer a wider range of engineering thermoplastics or even composites, but they also come at a steep price.

As the melted filament forms each layer, sometimes voids can remain between layers when they don’t adhere fully. This results in anisotropic parts, which is important to consider when you are designing parts meant to bear load or resist pulling.

The most common FDM 3D printing materials are ABS, PLA, and their various blends. More advanced FDM printers can also print with other specialized materials that offer properties like higher heat resistance, impact resistance, chemical resistance, and rigidity.

Stereolithography was the world’s first 3D printing technology, invented in the 1980s, and is still one of the most popular technologies for professionals. 

SLA parts have the highest resolution and accuracy, the clearest details, and the smoothest surface finish of all plastic 3D printing technologies. Resin 3D printing is a great option for highly detailed prototypes requiring tight tolerances and smooth surfaces, as well as functional parts, such as molds, patterns, and end use parts. SLA 3D printed parts can also be post-processed after printing by polishing, painting, coating, and more, resulting in client-ready parts with high-quality finishes.

Parts printed using SLA 3D printing are isotropic — their strength is consistent regardless of orientation because chemical bonds happen between each layer. This results in parts with predictable mechanical performance critical for applications like jigs and fixtures, end-use parts, and functional prototyping.

SLA 3D printing is highly versatile, offering resin formulations with a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics. Resin 3D printing also offers the broadest spectrum of biocompatible materials.

The specific material availability is highly dependent on the manufacturer and printer. Formlabs offers the most comprehensive resin library with 40+ SLA 3D printing materials.

Selective laser sintering (SLS) 3D printing is trusted by engineers and manufacturers across different industries for its ability to produce strong, functional parts. Low cost per part, high productivity, and established materials make the technology ideal for a range of applications from rapid prototyping to manufacturing aids, and low volume, bridge, or custom manufacturing.

As the unfused powder supports the part during printing, there’s no need for dedicated support structures. This makes SLS ideal for complex geometries, including interior features, undercuts, thin walls, and negative features. 

Just like SLA, SLS 3D prints are also generally isotropic. SLS parts have a slightly rough surface finish due to the powder particles, but almost no visible layer lines, and SLS 3D prints can be post-processed easily to further improve the mechancal performance and appearance.

The material selection for SLS is limited compared to FDM and SLA, but the available materials have excellent mechanical characteristics, with strength resembling injection-molded parts. The most common material for selective laser sintering is nylon, a popular engineering thermoplastic with excellent mechanical properties. Nylon is lightweight, strong, and flexible, as well as stable against impact, chemicals, heat, UV light, water, and dirt. Other popular SLS 3D printing materials include polypropylene (PP) and the flexible TPU.

Beyond plastics, there are multiple 3D printing processes available for metal 3D printing. 

• Metal FDM

Metal FDM printers work similarly to traditional FDM printers, but use extrude metal rods held together by polymer binders. The finished “green” parts are then sintered in a furnace to remove the binder. 

• Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) 

SLM and DMLS metal 3D printers work similarly to SLS printers, but instead of fusing polymer powders, they fuse metal powder particles together layer by layer using a laser. SLM and DMLS 3D printers can create strong, accurate, and complex metal products, making this process ideal for aerospace, automotive, and medical applications.

• Titanium is lightweight and has excellent mechanical characteristics. It is strong, hard and highly resistant to heat, oxidation, and acid.

• Stainless steel has high strength, high ductility, and is resistant to corrosion.

• Aluminum is a lightweight, durable, strong, and has good thermal properties.

• Tool steel is a hard, scratch-resistant material that you can use to print end-use tools and other high-strength parts..

• Nickel alloys have high tensile, creep and rupture strength and are heat and corrosion resistant.

Compared to plastic 3D printers, metal 3D printing is substantially more costly and complex, limiting its accessibility to most businesses.

Alternatively, SLA 3D printing is well-suited for casting workflows that produce metal parts at a lower cost, with greater design freedom, and in less time than traditional methods. 

Another alternative is electroplating SLA parts, which involves coating a plastic material in a layer of metal via electrolysis. This combines some of the best qualities of metal—strength, electrical conductivity, and resistance to corrosion and abrasion—with the specific properties of the primary (usually plastic) material.

With all these materials and 3D printing options available, how can you make the right selection?

Here’s our three-step framework to choose the right 3D printing material and plastic 3D printer for your application.

Plastics used for 3D printing have different chemical, optical, mechanical, and thermal characteristics that determine how the 3D printed parts will perform. As the intended use approaches real-world usage, performance requirements increase accordingly.

Once you’ve identified the performance requirements for your product, the next step is translating them into material requirements—the properties of a material that will satisfy those performance needs. You’ll typically find these metrics on a material’s data sheet.

For even more details on material properties, read our guide to about the most common mechanical and thermal properties.

Once you translate performance requirements to material requirements, you’ll most likely end up with a single material or a smaller group of materials that could be suitable for your application. 

If there are multiple materials that fulfil your basic requirements, you can then look at a wider range of desired characteristics and consider the pros, cons, and trade-offs of the given materials and processes to make the final choice.