FDM vs SLA: Choosing the Right 3D Printing Technology for Your Prototype, explained simply.
FDM and SLA are the two technologies you'll meet first when you start sourcing 3D printing for engineering work. They look similar in the marketing photos and feel completely different in your hand. This is when to pick which.
Core idea
What this blog covers
Teams default to whichever technology they've used before, then get burned when the project demands the other one. FDM Nylon doesn't replace SLA tough resin for fine threaded features, and SLA resin doesn't replace FDM PETG for parts that get dropped on a workshop floor.
Main discussion
How the two technologies actually work
FDM extrudes melted thermoplastic through a nozzle, layer by layer. The part is anisotropic — stronger along the layer plane than perpendicular to it. SLA cures liquid resin with a UV light, layer by layer. Parts are isotropic, surface finish is glass-smooth out of the printer, but build envelope is smaller and material range is narrower.
Where FDM wins
Functional engineering parts, mechanical brackets, fixtures, jigs, enclosures, drone frames, robotic linkages, snap-fits, anything load-bearing, anything that sees UV or weather. FDM also wins on cost-per-cubic-cm by 3-5x and on build volume — large parts (>200 mm) usually go FDM by default.
Where SLA wins
Fine-feature parts (sub-1 mm details, small thread profiles), jewellery masters, dental appliances, watertight prototypes, aesthetic prototypes where surface finish matters more than strength. SLA also has specialty resins — high-temp, elastomeric, biocompatible — that FDM can't replicate.
What about SLS, MJF, and other technologies?
SLS and MJF sit above both — Nylon parts that are stronger than FDM, smoother than FDM, and durable enough for end-use. The catch is cost: SLS / MJF parts in India start around ₹2,000 versus ₹200 for FDM. Use them when you need real production-grade Nylon and the volume justifies the price (typically 25+ units).
Our default decision tree at Yantrix
Functional or load-bearing? FDM — usually PETG, sometimes Nylon. Detail or finish-critical? SLA — usually tough resin. Outdoor or UV-exposed? FDM in ASA or PETG-CF. End-use Nylon at volume? SLS partner bureau. Watertight prototype? SLA every time. We confirm the choice as part of the DFAM review on every project.
Key takeaways
What readers should remember
- FDM = functional, cheap, large parts, real engineering thermoplastics. The default for most prototypes.
- SLA = fine detail, smooth surface, watertight, but brittle and UV-sensitive. The right pick for jewellery, dental, casting masters.
- Tolerance: SLA holds ±0.1 mm consistently; production FDM holds ±0.2 mm and hobby FDM around ±0.4 mm.
- If the part will live outdoors or under load for months, FDM in Nylon or PETG-CF is almost always the right answer.
Have a machine to build? Let's scope it together.
Tell us about your project. We'll respond within 1-2 business days with a preliminary scope and timeline — no boilerplate, no up-sell.