Short answer: FDM melts plastic filament and is the most affordable process for robust prototypes and fixtures. SLA cures liquid resin with light and delivers the finest details and smoothest surfaces. SLS sinters plastic powder with a laser, requires no support structures, and is suitable for durable functional parts and small-batch production. In practice, the „best“ process is not what decides, but rather the requirement of the part.
All three processes build a part layer by layer from a 3D file. The difference lies in the starting material and the way a layer solidifies. Everything else follows from this: surface finish, strength, post-processing, and cost.
Depending on the process and settings, the layer heights are between approximately 0.05 and 0.3 millimeters. This range is also mentioned in the guide How does a 3D printer work? our manufacturing. Resin printers operate at the lower end of this range, while FDM printers mostly operate in the middle and above.
No process wins in all categories. FDM wins in cost and simplicity, SLA in detail and surface finish, and SLS in design freedom and functional parts.
| Criterion | FDM | SLA | SLS |
|---|---|---|---|
| Starting material | Plastic filament | liquid synthetic resin | plastic powder |
| This is how the layer hardens | melt and deposit | cure with UV light | laser sinter |
| Typical materials | PLA, PETG, ABS, PA (nylon), fiber-reinforced variants | Standard, tough, flexible, and castable resins | above all PA12, plus flexible powders (TPE/TPU) |
| Surface | Layers visible | smooth, very fine details | even, slightly grainy and matte |
| Support structures | required for overhangs | almost always necessary | not necessary, the powder provides support |
| strength | good, but direction-dependent: weaker between the layers | depending on the resin, standard resins tend to be brittle | more uniform in all directions, resilient |
| rework | Remove supports, sand if necessary | wash, post-cure, remove supports | depowder, blast, dye if necessary |
| Occupational safety and health | low, ventilate with some materials | Gloves and safety glasses, do not get resin on the skin | Avoid dust, powder handling with extraction or mask |
| Initial device costs | low | low to medium | high |
| Machines in the academy | Qidi, Bambu Lab, Modix | Phrozen | Sintratec |
Regarding dimensional accuracy, we deliberately cite only one figure that we can substantiate: For FDM, our production specifies tolerances of ±0.2 to ±0.5 millimeters. For SLA and SLS, the value depends heavily on the machine, material, and part size. .
FDM is what you use when a part needs to be fast, inexpensive, and robust, and the surface finish is of secondary importance. It is the process with the lowest barrier to entry and the largest selection of materials. For standard materials like PLA, a nozzle operates at around 200 °C. Engineering plastics require significantly more and often a heated build chamber.
Typical components from our workshop practice:
You must know the most important weakness before you design: FDM parts are weaker between the layers than within a layer. A hook printed vertically will break at the layer boundary. Printed horizontally, the same hook holds a multiple of that. Orientation in the build space is therefore a design decision in FDM, not a slicer setting. That is one of the points we practice the longest in the FDM module.
Second weakness: overhangs require support structures, and where supports were placed, the surface suffers. Good designers avoid supports through chamfers, split components, or a different orientation.
You choose SLA when details and surface finish matter. Resin prints show fine text, sharp edges, and smooth surfaces that cannot be achieved with FDM. Layer lines are often barely visible to the naked eye.
Typical applications:
The price for this is the post-processing. A resin part comes out of the printer sticky. It is washed, usually in isopropanol or a cleaner specified by the manufacturer, and then post-cured under UV light. Only then does it have its final properties. Liquid resin is a hazardous substance: it must not get on the skin and not down the drain. Gloves, safety glasses, and ventilation are mandatory.
Standard resins are rather brittle. They are the wrong choice for snap-fit hooks or impact-loaded parts. Tough and flexible resins exist, but they cost more and require adjusted settings. In addition, some resins can undergo post-aging when exposed to sunlight. For functional parts used outdoors, we use FDM or SLS.
In the SLA module, you work on the Phrozen printers and learn two main things: how to orient and support parts so the print doesn't fail, and how to run the wash-and-cure process cleanly and safely.
SLS is used for durable functional parts, complex geometries, and small series. The decisive advantage: there are no support structures. The loose powder supports the part during printing. This enables shapes that are rarely successful with FDM and SLA: internal channels, interlocking moving parts, lattice structures.
The second advantage is capacity utilization. Because nothing needs to be supported, many parts can be nested on top of and inside each other within the build space. A single print job then delivers dozens of parts at once. That makes SLS interesting for small series production.
The standard material is PA12, a polyamide. The parts are tough, resilient, and more consistent in their properties across all directions than FDM parts. The surface is matte and slightly grainy. Those who need it smoother can bead blast or barrel finish it.
The disadvantages: The system is expensive, the process requires heat-up and cool-down times, and handling fine powder requires care. After printing, the powder cake is unpacked, and the parts are depowdered and blasted. Unsintered powder is sieved and reused mixed with fresh powder.
You will hardly find an SLS system in any hobby workshop. The fact that you prepare, unpack, and post-process a print job yourself on a Sintratec at the academy is therefore the part of your training that you could least teach yourself.
Ask four questions in this order. Usually after the second question, it's clear where it's going.
An example: A mount for a sensor on a machine. It just needs to hold, nobody looks at it, and a single piece is needed. That is FDM in PETG or a tougher material. The same mount in a quantity of 200 with an integrated snap-fit hook is an SLS case. The presentation model of the same sensor for the trade fair is SLA.
Because process selection is the first technical decision in any project. Anyone who only knows FDM solves every problem with FDM, even if it is the wrong tool. Companies are looking for people who can read an inquiry and say: We will print it like this, from this material, in this orientation, and that is how much post-processing is involved.
That is why our three advanced training courses are structured according to the processes. Each comprises 600 teaching units over 60 days, divided into an FDM, an SLA, and an SLS module, each with 200 teaching units over 20 days. In each module, you spend one week in the workshop in Altenholz near Kiel. The main focus varies depending on the direction: Manufacturing manager, Product Designer or Designer. Those who are just looking for a compact overview with practical application are in the two-week IHK certificate course Right.
FDM. Equipment and materials are inexpensive, occupational safety is simple, and you learn the basics of slicing and alignment, which you will also need for the other processes.
For fine details and surfaces, yes. For the dimensional accuracy of large parts, not automatically, because resins shrink during curing and thin walls can warp. In all processes, accuracy depends heavily on orientation and the specific process.
The unsintered powder remains in the build chamber and supports the component. As a result, overhangs and cavities always rest on powder.
No. FDM, SLA, and SLS in the form described here are plastic processes. Metal is printed using other processes, for example by laser melting of metal powder. That is not part of our continuing education programs.
FDM is the affordable workhorse for robust prototypes, jigs and fixtures, and large parts. SLA delivers the finest details and smooth surfaces, but requires working cleanly with resin. SLS requires no supports and is the first choice for heavy-duty functional parts and small series production. Anyone who knows all three processes firsthand can make the right choice in minutes. That is precisely what we practice in one module of 200 instructional units each.
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Author: Editorial team of the Mach-3D Academy · Last updated: September 2026
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