A bracket you bolt on once to check hole spacing, a presentation model a client will hold, and a clip that flexes every time a lid comes off need three different 3D printing processes. FDM (fused deposition modeling) is the cheap, quick choice for the bracket, SLA (stereolithography) gives the model its finished surface, and SLS (selective laser sintering) makes a nylon clip tough enough to last. Every FDM vs SLA vs SLS decision works the same way: the right process follows from what the part has to survive.
Picking wrong costs you twice. Layer lines on an FDM model can sink a pitch meeting, and an SLS batch ordered for a single fit check spends money a cheap print would have covered. Five factors decide most jobs, and no process wins all five.
FDM vs SLA vs SLS on the Five Factors That Decide Most Jobs
All three build a part one layer at a time, but they start from different raw material: FDM extrudes melted plastic filament, SLA cures liquid resin with light, and SLS fuses nylon powder with a laser. For the mechanics of each step, from file to finished part, see our pillar guide on how 3D printing works. For choosing between them, these are the factors that matter:
- Cost per part: FDM is usually the cheapest way to get a simple part in small numbers, and SLA costs more. SLS has the highest setup cost, but it needs no supports and packs many parts into one build, so it often comes out cheapest for complex shapes and fuller batches.
- Surface: SLA gives the smoothest surface of the three and holds embossed detail down to about 0.1 mm, where FDM needs raised features around 0.6 mm wide before they read clearly. SLS comes out matte and slightly grainy, which is fine on a working part.
- Strength: SLS nylon and engineering-grade FDM plastics take real loads. Some standard SLA resins are brittle, and some SLA materials degrade with long exposure to UV (ultraviolet) light, though tough and engineering resins close part of that gap.
- Geometry: SLS needs no supports, because the loose powder holds the part, so internal channels and undercuts come out clean. FDM and SLA need supports under overhangs, which leave marks to sand off and limit some internal shapes.
- Finishing time: Print time alone is misleading. SLA parts come off the printer only partly cured and need an alcohol wash and a post-cure, an SLS build has to cool in its powder for hours before the parts come out, and supported FDM parts need their supports cut away and the marks sanded.
Rank those five for your part and the top item usually picks the process for you. For anything a client will see, cost is rarely the right thing to put first.
SLA vs FDM: Which Is Better for Your Part?
Both processes are easy to find, and both produce a rigid plastic part from the same CAD (computer-aided design) file, so the choice can feel arbitrary. The deciding question is whether the part gets looked at or handled. Choose SLA when it will be seen or has small features, and FDM when it will be tested, handled roughly, or set aside after a fit check.
SLA’s smooth surface makes it the better choice for presentation models, detailed housings, and master patterns for silicone molds. Silicone copies fine surface detail, defects included, so a pattern printed in FDM leaves its layer lines in every cast part. The trade-off is toughness. Because some standard resins are brittle, we would print anything that flexes in service, such as a snap tab, in a tough resin or in SLS nylon.
FDM earns its place on material cost and choice. Filament is the cheapest raw material of the three, which adds up on a large part, and tough thermoplastics such as PETG (polyethylene terephthalate glycol) and nylon are common options. Its weak spot is the bond between layers, which is why a part loaded across its layers fails well below the plastic’s rated strength. Orientation and design choices for load-bearing parts are covered in our guide to functional 3D printing.
SLA vs SLS: When Does Nylon Beat Resin?
SLA and SLS both produce parts good enough to show a client, which is why this comparison comes up once a project moves past rough prototypes. The split is simple: SLA gives the better surface, and SLS gives the tougher part. If the part will be painted and looked at, print it in SLA. If it clips, flexes, or takes knocks, print it in SLS nylon.
SLS also wins on geometry. The loose powder holds the part for the whole build, so internal ducts, undercuts, and thin walls come out with no support scars. SLA needs a support under every overhang, and each attachment point leaves a small nub that has to be sanded off before paint.
The other SLS advantage is batch cost. Dozens of small parts can be nested, packed together in three dimensions, into a single build, and the cost per piece drops as the build fills. Forty snap-fit clips from one SLS build need no support cleanup, which is why SLS works well as a low-volume bridge before paying for an injection mold.
Four Common Parts and Where We Would Print Them
Requirements are easier to judge with a real part in mind. Here is where we would send four common jobs, and why each one lands where it does:
- A bracket to check fit against an existing assembly: FDM. The job is confirming hole spacing and clearances, so the cheapest print that holds the dimensions wins, and a revised version costs little.
- A presentation model for a pitch meeting: SLA. Support marks come off with light sanding before primer and paint, and button edges and embossed logos stay crisp.
- Forty snap-fit enclosures for a pilot run: SLS. The clips need nylon’s toughness to survive repeated assembly, and the whole batch fits in one build.
- A master pattern for silicone mold casting: SLA. Any layer line on the pattern transfers to every casting, so the smoothest possible start saves hand finishing across the run.
A single product can move through all three. We would use FDM for early fit checks, SLA for the pitch model, and SLS for the pilot batch, because matching each stage to its process costs less than forcing one technology through the whole program.
What to Send Us for a Straight Answer
Describe the part’s job instead of naming a process. The details that settle it are what the part attaches to, the loads and temperatures it sees, how it has to look, how many you need, and your deadline. With those in hand, the FDM vs SLA vs SLS choice usually settles in one conversation.
Our 3D printing services run all three processes, and we also offer CNC (computer numerical control) routing, molding, and casting, so if printing is the wrong answer for your part we will say so. Send a CAD file or a sketch through our contact page, or call 718-557-9578 with the part’s job and quantity, and we will tell you which process fits and what it will take.
