SLA vs. PolyJet 3D Printing: In-Depth Comparison
There are many 3D printing processes on the market. Getting familiar with the nuances of each helps to clarify what you can expect from final prints to ultimately decide which technology is suitable for your particular application.
PolyJet and stereolithography (SLA) are two common processes for resin 3D printing. Both technologies are popular for producing high-accuracy, isotropic, and watertight industrial-quality prototypes and parts in a range of advanced materials with fine features and a smooth surface finish.
In this comprehensive guide, we take a closer look at PolyJet and SLA 3D printers, and how they compare in terms of costs, print quality, materials, applications, workflow, speed, and more, to help you decide which technique is ideal for your business.
What is PolyJet 3D Printing?
PolyJet belongs to the family of material jetting additive manufacturing processes. The technology was developed by Objet, which was later acquired by Stratasys. There are other material jetting printers on the market, but under the brand name PolyJet, they are only sold by Stratasys.
PolyJet 3D printers work similarly to traditional inkjet printers, but cure drops of photopolymer plastic instead of jetting droplets of ink. During printing, a print head moves across the build platform along the X and Y axis, jetting out droplets of resin onto the platform. Within the same movement, ultraviolet light from the print head cures the droplets on the build platform. After the layer is complete, the built platform moves down, so that the print head can distribute a second layer. The printed object will then continue to grow until the process finishes.
For more complex geometries such as overhangs, the 3D printer jets a removable gel-like support material. The print heads can also mix multiple materials together to achieve unique material properties and colors.
What is SLA 3D Printing?
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 3D printers use a laser to cure liquid resin into hardened plastic in a process called photopolymerization.
SLA 3D printers contain a resin tank with a transparent base and non-stick surface, which serves as a substrate for the liquid resin to cure against, allowing for the gentle detachment of newly-formed layers.
The printing process starts as the build platform descends into a resin tank, leaving space equal to the layer height in between the build platform, or the last completed layer, and the bottom of the tank. A laser points at two mirror galvanometers, which direct the light to the correct coordinates on a series of mirrors, focusing the light upward through the bottom of the tank and curing a layer of resin. The cured layer then gets separated from the bottom of the tank and the build platform moves up to let fresh resin flow beneath. The process repeats until the print is complete.
Low Force Stereolithography (LFS) technology, used by the Form 3+ and Form 3L, is the next phase in SLA 3D printing. In LFS 3D printers, the optics are enclosed in a Light Processing Unit (LPU). Within the LPU, a galvanometer positions the high-density laser beam in the Y direction, passes it through a spatial filter, and directs it to a fold mirror and parabolic mirror to consistently deliver the beam perpendicular to the build plane and ensure accurate, repeatable prints.
As the LPU moves in the X direction, the printed part is gently peeled away from the flexible bottom of the tank, which drastically reduces the forces exerted on parts during the print process.
This advanced form of stereolithography delivers vastly improved surface quality and print accuracy. Lower print forces also allow for light-touch support structures that tear away with ease, and the process has opened up a wide range of possibilities for advanced, production-ready materials.
Introduction to 3D Printing With Desktop Stereolithography (SLA)
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PolyJet vs. SLA: In-Depth Comparison
While PolyJet and SLA 3D printers both create high-resolution resin parts, there are various benefits and drawbacks for specific applications. As such, it is helpful to evaluate their comparative strengths and weaknesses in a few key categories.
Costs and Return on Investment
One of the main differences between PolyJet and SLA printers involves costs. As SLA patents began to expire at the end of the 2000s, and smaller format, desktop SLA 3D printers were introduced to the market, the cost of SLA printers decreased by 100x. Today, prices for professional SLA printers start at about $3,750, while large format benchtop printers start at $11,000.
In contrast, PolyJet printers are substantially more expensive, with prices ranging from $30,000 to $500,000+. This is only the machine cost, compulsory service plans can cost up to 20% of the price of a PolyJet printer annually, which is enough to buy a fleet of SLA printers each year.
In addition, PolyJet materials are generally two to three times more expensive than SLA resins. As a result, the overall cost per part for PolyJet prints is many times higher than that of an SLA print. PolyJet printers also require more maintenance, increasing the amount of labor necessary to operate these machines.
Thus, unless you specifically need PolyJet for a certain application, such as full-color models or multi-material parts, you are likely to see a higher return on your investment with an SLA printer.
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Print Quality and Precision
Because 3D printing is an additive process, each layer introduces an opportunity for inaccuracy, and the process by which layers are formed affects the level of precision, defined as the repeatability of the accuracy of each layer. 3D printing tolerances, accuracy, and precision depend on many different factors: the 3D printing process, materials, software settings, post-processing, and more.
Both PolyJet and SLA 3D printers are among the most accurate and precise 3D printing processes, with tolerances around ± 0.2% (lower limit: ± 0.1 mm). Thanks to the highly-precise light sources, these processes can achieve fine details and can consistently produce high-quality results.
Depending on the model geometry, PolyJet and SLA 3D printed parts require support structures, which can be essential to achieve dimensional accuracy, especially with complex geometries or large and thin walls.
With SLA, supports are removed manually during post-processing. Formlabs LFS printers offer enhanced light touch support structures that detach from parts in seconds to save post-processing time. SLA printed parts are also known for their smooth surface finish, which, depending on the material, can be matte or glossy.
With PolyJet printers, support structures are washed away during post-processing with a water jet. This workflow exerts forces on the parts and can break intricate details or bend thin walls. PolyJet printers can print with a matte and glossy surface. However, glossy finish is only limited to sections of the model, where support material is not used.
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Materials and Applications
One of the biggest differences between PolyJet and SLA is the availability of materials, which also defines the possible applications for these printers.
Depending on the printer model, most PolyJet 3D printers support around five to ten different materials. These range from standard prototyping materials, to materials in different colors, clear materials, and biocompatible materials. More high-end PolyJet 3D printers also support printing with multiple materials at the same time, enabling novel applications such as printing multicolor and multi-material prototypes.
However, PolyJet printers can only print with low-viscosity materials, which severely limits the range of properties available. PolyJet materials also have a low heat deflection temperature (HDT), generally around 45-50 °C, which means that they can even start to creep and lose shape under strong light. As a result, PolyJet printing is only ideal for concept modeling and non-functional prototyping applications, as well as some dental and medical applications that require biocompatibility.
SLA 3D printers support a much wider range of materials than a typical PolyJet printer, with up to 30+ materials for Formlabs 3D printers. SLA resins can be flexible or stiff, clear or opaque, heavily filled with secondary materials like glass, wax, or ceramic, or imbued with mechanical properties like high heat deflection temperature or impact resistance.
SLA materials can closely match common end-use thermoplastic materials for rapid prototyping, with specific materials formulated to be soft-touch, thermally and chemically resistant, highly durable, or dimensionally stable under load. SLA 3D printing also offers the widest range of biocompatible materials for dental and medical applications.
Find the Right Material for Your Application
Need some help figuring out which 3D printing material you should choose? Our new interactive material wizard helps you make the right material decisions based on your application and the properties you care the most about from our growing library of resins.
Workflow and Ease of Use
The workflow for both PolyJet and SLA 3D printing consists of three steps: designing, 3D printing, and post-processing.
See how to go from design to 3D print with the Form 3+ SLA 3D printer.
First, use any CAD software or 3D scan data to design a model, and export it in a 3D printable file format (STL or OBJ). 3D printers then require print preparation or slicer software to specify printing settings and slice the digital model into layers for printing.
Both PolyJet and professional SLA 3D printers come with their own proprietary software and predefined settings for each material that have been thoroughly tested to ensure the highest print success rate.
Setting up prints with advanced print preparation tools like PreForm is plug-and-play. PreForm is a free download, try it now.
Once the 3D printing process begins, 3D printers can run unattended, even overnight, until the print is complete. Both PolyJet printers and advanced SLA 3D printers like the Form 3+ and the Form 3L offer a cartridge system that refills the material automatically.
To post-process parts, you will need to manually remove support material from a PolyJet printed part using a water jet or a combination of chemical baths and peeling for thick supports. This can bend parts with thin walls and also easily break delicate features. PolyJet parts don’t require post-curing—the models come off the printer fully cured.
PolyJet printers often require more maintenance than a typical SLA printer. You will need to clean the print head, build tray, and roller after every use. In addition, you will need to clean the UV lamps and wiper daily and perform regular tests to ensure that your printer remains in working condition.
PolyJet printers also require setup and training with on-site installation. The more complex workflow and the steeper learning curve mean that the system requires a skilled technician in-house to operate and maintain.
SLA parts require rinsing in isopropyl alcohol (IPA) or alternative solvents to remove any uncured resin from their surface. Using the standard workflow, this involves first removing parts from the build platform, then manually soaking them in a bath of solvent to clean off excess resin.
Professional solutions such as the Form Wash and the Form Wash L automate this process. Parts can be transferred directly from the printer to Form Wash or Form Wash L, which agitates the solvent around the parts to clean them and automatically raises parts out of the alcohol bath when the process is finished.
After rinsed parts dry, some SLA materials require post-curing, a process that helps parts to reach their highest possible strength and stability. This can also be automated with curing solutions like the Form Cure and the Form Cure L.
Support removal for SLA parts requires cutting away the support structures and lightly sanding the parts to remove support marks. Formlabs’ Low Force Stereolithography (LFS)™ technology offers light-touch supports, which allow an entire object to be torn away from its support base in seconds, leaving minimal markings and reducing time spent post-processing.
Besides keeping the printer and the work area tidy, professional SLA 3D printers generally don’t require regular maintenance. The easy workflow also empowers anyone at a company to use an SLA printer independently after less than one hour of training.
When further post-processing is required, both PolyJet and SLA parts can be machined, primed, painted, and assembled for specific applications or finishes.
Hands-on Demo: The New Form 3+ and Build Platform 2
In this webinar, Matt Lewis and Ricky Hopper walk you through an overview of the improved SLA line, and give a hands on demo of the new products.
PolyJet printers are available in various sizes, from smaller benchtop models to large multi-ton industrial machines. Due to the differences in technology, developing larger PolyJet machines is less complex.
The first SLA 3D printers were mainly large industrial machines that offered large build volumes, but often at an even higher cost than PolyJet and with a much more complex workflow. However, thanks to the rapid development of the SLA printing technology, SLA printers are now available in both compact desktop and large format benchtop forms.
The inverted SLA process behind more accessible desktop and benchtop SLA printers reduces footprint and cost, but heightened peel forces introduce limitations around materials and build volume, and larger parts would require sturdy support structures to print successfully.
With the introduction of the Low Force Stereolithography (LFS) print process that powers the Form 3 and Form 3L, Formlabs has completely re-engineered the approach to resin-based 3D printing to drastically reduce the forces exerted on parts during the print process. Uniform linear illumination and the low forces from the flexible tank mean LFS technology can seamlessly scale up to a larger print area built around the same powerful print engine.
The first affordable large format resin printer, the Form 3L, delivers large parts fast, using two staggered light processing units (LPUs) that work simultaneously along an optimized print path. Delivering a build volume five times larger than current SLA printers, the Form 3L removes size restrictions that sometimes hinder workflows on smaller desktop devices, while maintaining a competitive price point.
Form 3L Ecosystem Demo
Want to learn more about the Form 3L and Form 3BL ecosystem, and the new large format post-processing machines? In this demo, Kyle and Chris will expain how to navigate the Form 3L end-to-end workflow, including post-processing.
Both PolyJet and SLA are considered some of the fastest 3D printing technologies.
PolyJet 3D printers provide very fast printing speeds within a five-inch cube, but for larger models and builds the printing speed slows down significantly as the print head has to travel farther, which causes the layers to take a longer amount of time to complete. Lasers and galvanometers in SLA printers are just as fast for large builds as well as small builds.
PolyJet printers also have a limited range of automated post-processing solutions available, so while the actual printing process may be faster, post-processing is often slower and more labor-intensive with a PolyJet printer.
Speed can also depend on the material choice. Printing four times faster than Formlabs standard SLA materials, Draft Resin is a fast-printing resin that is ideal for initial prototypes, rapid iterations, as well as dental and orthodontic models. From fast print initiation speeds to minimal support removal, wash, and cure times, Draft Resin has an optimized workflow to truly maximize efficiency.
PolyJet vs. SLA: Side by Side Comparison
Each 3D printing technology has its own strengths, weaknesses, and requirements, and is suitable for different applications and businesses. The following table summarizes some key characteristics and considerations when comparing PolyJet vs. SLA 3D printers.
|Ease of Use||★★★★☆||★★★★★|
Smooth surface finish
Color 3D printing
Fast printing speeds (for small parts)
Smooth surface finish
Fast printing speeds
Wide range of functional applications
|Cons||Expensive machinery and materials|
Limited material options
Parts are sensitive to heat and long exposure to UV light.
Requires maintenance and a dedicated operator
|Parts are sensitive to long exposure to UV light|
Looks-like (non-functional) prototypes
Dental and medical applications
|Looks-like and functional prototyping|
Patterns, molds, and tooling
Dental and medical applications
Jewelry prototyping and casting
|Build Volume||294 x 192 x 148.6 mm for benchtop printers, up to 1000 x 800 x 500 mm large-scale printers||145 × 145 × 185 mm for desktop printers, up to 300 x 335 x 200 mm for benchtop 3D printers|
|Price||Benchtop printers start around $30,000, large-scale industrial machines can cost $500,000+.||Professional desktop printers start at $3,750, large format benchtop printers at $11,000, and traditional large-scale industrial machines are available from $80,000.|
|Materials||Varieties of resin (thermosetting plastics). Standard (opaque, clear, colors), engineering, dental and medical (biocompatible)||Varieties of resin (thermosetting plastics). Standard (opaque, clear), engineering (ABS-like, PP-like, flexible, heat-resistant, high-strength, and more), castable, dental and medical (biocompatible)|
Choosing the Right 3D Printer for Your Needs
Both PolyJet and SLA 3D printing technologies have unique benefits, from high accuracy and precision, to a smooth finish, fast prints, and high-performance materials. However, SLA technology has evolved faster and provides unique benefits, especially considering the cost, ease of use, and the possible range of applications.
Formlabs offers two high-precision SLA 3D printing systems, a growing library of specialized materials, intuitive print preparation and management software, and professional services—all in one package. Curious to see the quality firsthand? Order a sample part shipped to your office.