There are a lot of different materials available for 3D printing, and it can be difficult to know which will best suit your needs. In this article, we’ll discuss the four main categories of 3D printing materials, their properties, how they’re produced, and their best uses. 

Extruded Thermoplastics

Extruded thermoplastics are what typically come to mind when someone thinks of 3D printing. Their rigidity and durability have contributed to their wide use in a variety of industries, making them the most common 3D printing materials available. Depending on the specific thermoplastic, there are additional mechanical properties that make them desirable for every day use, including heat resistance, fatigue resistance, high tensile strength, high flexural strength, low weight, electrical-dissipation, and more. Some can even simulate the appearance and feel of rubber. Common 3D printing thermoplastics include ABS-M30, ABS-ESD7, PC-ABS, Polycarbonate, PPSF, ULTEM 9085, Nylon 12, and TPU. 

In order to print this type of material, thermoplastic filament is fed from a spool through the print nozzle of a Fused Deposition Modeling (FDM) 3D printer. Here, it is melted and extruded onto a build platform. The print head uses the liquefied material to draw the first layer of the part to be printed. As layers are added, the material bonds together with lower layers to produce a strong, 3D printed part. Support material is also used to help build the part, especially in areas with overhangs or freestanding features, and is removed in post-processing. Support materials may be soluble or break-away depending on the heat deflection temperature of the thermoplastic being used. 

Best Applications

• Functional Parts – The strength and durability of most thermoplastics make them the ideal material for functional prototypes, especially where designs must be evaluated before injection molding. Low-volume productions of end-use parts may also be made with these materials. 
• High Temp – Most thermoplastics can withstand elevated temperatures without deformation or loss of strength. Some can be used to create molds for low-volume thermoforming. 

Photopolymers

Photopolymers are liquid resin thermosets that cure when exposed to UV light. Because they are thermosets, this means they will not melt as thermoplastics do. Instead, most will burn when exposed to extreme heat. These materials can often be produced in a range of shore values, allowing for them to simulate anything from soft rubber to hard plastic. Some are flexible, giving the appearance of elastomers. Others are heat and moisture resistant for use in humid applications. While these materials are versatile, they should not be used outdoors because further exposure to UV light after curing can damage the part.

Photopolymers may be 3D printed with three different technologies: PolyJet, MultiJet, and Stereolithography (SLA). 

PolyJet 3D printing deposits liquid photopolymers onto a build tray using a print head with a dot grid. Droplets are deposited in the shape of each layer and cured by a UV light. A wax-like material is used as support and is dissolvable in a lye solution. Some additional post-processing may include scraping, peeling, and washing away residue. PolyJet is capable of blending photopolymer resins to create varying shore values, which can simulate both plastic and rubber. Common PolyJet photopolymers include Rigur, Tango, Digital ABS, Vero, RGD720, and RGD525.

MultiJet 3D printing works in a similar fashion as PolyJet, depositing the photopolymer material with a dot matrix print head and curing each layer with UV light. However, MultiJet material does not begin in a liquid state and must be heated prior to deposition. Its wax-like support material also differs from PolyJet in that it must be melted away in an oven. This enables a part with blind cavities to be printed properly without concern of removing support manually and causing damage. To remove residue, a part printed with this technology will be processed through an ultrasonic bath, cleanse, and a final rinse. Common MultiJet photopolymers include VisiJet M3-X, VisiJet M3 Black, VisiJet M3 Crystal, VisiJet M3 Proplast, VisiJet M3 Navy, VisiJet M3 Techplast, and VisiJet M3 Procast. 

SLA 3D printing also deposits liquid photopolymers onto a build tray, except that it does so across the entirety of the surface, not in the shape of the layer as with PolyJet and MultiJet. Rather, a UV light is directed with mirrors to trace the shape of the layer in the resin. Wherever this UV light is aimed, the photopolymers are cured and solidified. Once the part is completed, it will be sitting submerged in the vat of uncured resin. As for support structures, they are made from the same photopolymer resin used to create the part. They are clipped off in post-processing, and the part goes through additional steps to further harden the resin and sand and rinse it. Common SLA photopolymers include Somos PerFORM, Somos ProtoGen 18420, Somos WaterClear Ultra 10122, Somos WaterShed XC 11122, Somos NeXt, SC 1000P, and Somos Element. 

Best Applications

• Cosmetic Prototypes – The high resolution and smooth surface finish that photopolymers produce make them perfect for creating cosmetic prototypes. 3D printed photopolymers can mimic the appearance of injection molded parts, enabling you to see what they will look like before investing in expensive tooling. Any of the three technologies above will produce satisfactory cosmetic results. 
• Fit Testing – Photopolymers are more controlled during the printing process than thermoplastics and are produced with tight tolerances. As such, these materials work great for fit testing, especially with intricate components, such as electrical connectors. MultiJet produces the best results for fit testing. 
• Flexible Parts – PolyJet 3D printing can blend different types of photopolymers to create different shore hardnesses and varying degrees of flexibility. Parts produced via SLA, however, are brittle and will break under similar stress. 

Powdered Thermoplastics

Powdered thermoplastics exhibit many of the same characteristics of extruded thermoplastics. Their high strength, heat resistance, impact resistance, chemical resistance, wear resistance, flame retardancy, low moisture absorption, and electrical-dissipation qualities have led to frequent use in the electrical, automotive, and aerospace industries. Some powdered thermoplastics may also be produced with varying shore values to be slightly flexible. Many of this class of thermoplastics are varying grades of Nylon with additives like carbon fiber or aluminum. Common powdered thermoplastics include Flex TPE, Nylon 11 EX, Nylon 11 FR, Nylon 11, Nylon 12 PA, Nylon 12 FR, Nylon 12 GF, Nylon 12 CF, Nylon 12 GSL, Nylon 12 HST, and Nylon 12 AF. 

These materials are produced via a process called Selective Laser Sintering (SLS). This involves the 3D printer depositing a layer of powdered material over the entirety of the build platform. A high-powered laser is then aimed at the powder, which heats it until the edges of the powder grains fuse together. The laser traces the layers of the part, sintering the material as it does so, and the build platform lowers after each one is completed so that a new layer of powder can be deposited to begin the next one. No support material is needed for parts produced via SLS. The unsintered powder acts as a cake or cushion around the part, and this excess is dusted off in post-processing. An important note about SLS 3D printing is that the powder will not be fully melted during the process, which means parts will be about 30% porous. 

Best Applications

• Functional Parts – The strength of powdered thermoplastics make them a practical material to use for both functional prototypes and end-use parts. These materials can also be dyed and finished to fit the desired appearance. 
• High Temp – Powdered thermoplastics can withstand similar temperatures as extruded thermoplastics. Some grades are even flame, smoke, and toxicity certified, making them well suited for extreme heat applications.

Metals

Although metal is most commonly machined, it can also be 3D printed. While metals are the strongest 3D printing material, they are also the most expensive, which is why plastic is the preferred material type for most 3D printed parts. 3D printing metals come in a powdered form just as the materials for SLS. The metals retain the same mechanical properties as if they were machined, including high strength, heat resistance, corrosion resistance, weldability, and ductility. Some 3D printing metals are biocompatible, which enables them to be used in the dental and medical fields in addition to the oil, gas, and automotive industries. Common 3D printed metals include Stainless Steel 17-4 PH, Stainless Steel 316L, Aluminum AlSi10Mg, INCONEL 625, INCONEL 718, Titanium Ti64, Cobalt Chrome CoCrMo, MONEL K500, and Copper C18150. 

Metals are 3D printed via Direct Metal Laser Sintering (DMLS), which is a process nearly identical to SLS. The primary difference is that DMLS full melts the powder so that the material will bond to create a homogenous part. This produces stronger, high density parts with less porosity. Another difference is that since metal is more dense than most thermoplastics, support structures must be used to build the part. In post-processing, these must be clipped off after a heat-treat cycle to relieve stress in the part. Without this heat-treat cycle, the part may distort, warp, delaminate, or crack during further post-processing and use. DMLS also leaves a grainy surface finish that is commonly bead blasted and deburred to achieve a smooth finish. 

Best Applications

• Cosmetic Prototypes – 3D printed metal parts are bead blasted in post-processing to get a smooth, clean surface finish that results in an aesthetically pleasing part. Producing a prototype this way is especially helpful if you are planning to machine the part later and need to see a late-stage cosmetic prototype before you start production. 
• Fit Testing – Once the grainy surface of a 3D printed metal part has been smoothed, parts can be used for precise fit testing. 
• Functional Parts – Metal has extreme strength, which means it can be used for many applications where plastic will not be satisfactory. Many of the above materials will support high loads and have a high strength-to-weight ratio.
• High Temp – Most metals can withstand extreme heat and demanding working conditions. This is why metal is the most common material used in the automotive and aerospace industries. 

3D Printing at 3 Space

Here at 3 Space, we offer a variety of extruded thermoplastics and photopolymers on our top-of-the-line industrial grade FDM, PolyJet, and MultiJet 3D printers. If you are unsure which material may be best suited for your part, our engineers are happy to assist you and make recommendations based on your part’s intended use. For more information, contact us today.