There are many factors that influence whether or not a given material will function on a Formlabs SLA printer. Print reliability, print speed, surface finish, accuracy, and fine feature resolution are all factors that can be influenced by material selection, 3D printer, and your settings in the Print Settings Editor. Not all factors that influence these are immediately obvious, and even some materials that meet the requirements described below can still fail to print.

As a general rule of thumb, if the material is designed to UV cure with 405 nm light, there is a good chance you will be able to print with it on a Formlabs SLA printer such as the Form 4. All other considerations are secondary.

The most important single factor for determining if a resin will print with Formlabs SLA printers is the wavelength that it is designed to work with. Formlabs printers use 405 nm wavelength light, which is one of the most common wavelengths used in photopolymerization 3D printing. Other common wavelengths are 385 nm and 450 nm. There is some overlap between these depending on the exact photoinitiators used, but if the manufacturer of the given resin uses a wavelength other than 405 nm, it bears digging more into the resin properties to see if it will print successfully on a Formlabs machine.

If the product does not indicate the wavelength, you can purchase a 405 nm laser pointer and expose a droplet of the resin to the laser to see if it cures. Another option is to pour a small pool of resin into a clean resin tank, run the cleaning sheet tool on the printer, and evaluate if the resin cured. If the resin does not cure in these tests, it is unlikely to work on a Formlabs SLA printer. If it does cure, it is fairly likely to be printable, but the quality, reliability, and print speed still need to be evaluated.

If the resin is not designed for 405 nm light or the default exposure values, you may see the following print failures:

• Parts come out undercured: Parts are very tacky and floppy (i.e., low strength in the green state). This usually means that the resin requires a higher exposure to print properly.
• Parts have increased Z bleed: There is more curing than desired per layer, so each layer is thicker than intended. Holes may not come out round and small features are often oversized.
• Nothing cures: Even with a high exposure, no curing or almost no curing occurs and the part does not form.

While wavelength is by far the most important property, there are some other properties that can affect the printability of a material. These properties usually influence the quality of the print.

Viscosity

The viscosity of a resin is a measure of the resistance it has to flow, often given in centipoise, or cP. For example, water is a low viscosity material that flows quickly, while molasses is a high viscosity material that flows extremely slowly. This can have a significant impact on the printability of a resin. Resins that have very low viscosity can be prone to splashing onto the sides of the printer, while resins that are extremely viscous require slow motor moves to allow the resin to fully coat the print surface and to avoid excessive forces on the part.

Formlabs printers have successfully printed with resins between 100 and 30,000 cP, though there is no hard limit to the range of printability. Generally, lower viscosity resins are preferred, with resin viscosities in the range of a few hundred cP. High-viscosity resins impose higher forces on the printer and your printed parts, which can cause motor or wiper stalls, uneven layers, or other defects that seriously affect print quality. For reference, Silicone 40A Resin is currently the most viscous resin Formlabs produces, at 7,800 cP.

Temperature can dramatically change viscosity, with higher printing temperatures resulting in a lower viscosity. Formlabs SLA printers can operate at up to 45 °C, which can make printing significantly faster and lower the risk of print failures. Note that heating the resin can extend pre-print times and cause extra fumes if your selected resin volatizes easily.

Some common print failures that are related to resin viscosity are:

• High viscosity resin may create excessive forces while lowering the build platform, which may result in deflection of the build platform and thicker or slightly uneven layers.
• High viscosity resin may not completely recoat the print surface between layers, leading to missing or incomplete features.
• Low viscosity resin may splash out of the resin tank onto the interior of the printer.

Mechanical properties

Formlabs printers can print with resins with a wide variety of different mechanical properties, but there are some important factors to keep in mind. Softer materials are generally more difficult to print, requiring slower motor moves to reduce forces on the part and more supports to ensure stability. Generally, if the material has a modulus of 1500 MPa or higher, it is going to be relatively easy to print with, while softer materials can be more challenging.

Physical properties

Some other physical properties are worth noting, depending on the exact material:

• Additive/filler powder or particle size: Large particle sizes, especially larger than a layer height, can have a severe effect on printing. If the resin has an additive whose particle size is larger than your selected layer height, you run the risk of damaging the resin tank film or the printer itself when squishing a layer down. Particle morphology plays more of an effect on mechanical properties, where if particles are longer in a particular direction, that will tend to randomly orient in the XY plane, rather than remaining isotropic.
• Additive/filler powder or particle morphology: If the resin has an additive whose particles are longer in a particular direction, they will tend to orient themselves in the XY plane rather than remaining isotropic.
• Filler translucency: Even resins that cure well with 405 nm light can fail if filled with a filler material that blocks light. Resins with less translucent fillers may still print with smaller layer heights, since the light has a shorter path to travel before curing a layer.
• Chemical compatibility: Some types of materials may react with the resin tank, the tank film, or some other part of the printer. Check for any unexpected reactions prior to printing, as well as periodically throughout the printing process.
• Safety: Always read the manufacturer’s safety data sheet (SDS) before handling any new materials. Be aware of printing temperature as this can exacerbate evaporation of resins. Use appropriate precautions, ventilation, and personal protective equipment when working with resins.