Every additive process builds a part layer by layer from a digital model, but the way each layer forms decides resolution, strength, material choice, and cost. Choosing the wrong process wastes weeks of iteration. This guide compares the five processes engineering teams use most. How the layer forms decides everything Fused deposition modeling extrudes molten thermoplastic. Stereolithography and digital light processing cure liquid photopolymer with ultraviolet light. Selective laser sintering fuses polymer powder with a laser. PolyJet jets and UV-cures droplets of photopolymer. That single mechanical difference drives every downstream trade-off, from surface finish to the anisotropy of the finished part. Fused deposition modeling Strengths: low machine and material cost, wide thermoplastic range including PLA, ABS, PETG, nylon, and filled composites, simple workflow Limits: visible layer lines, 100 to 300 micron typical layer height, weak Z-axis strength, support removal on overhangs Best for: early form-and-fit prototypes, jigs and fixtures, large low-detail parts Stereolithography and digital light processing Strengths: 25 to 100 micron layers, smooth surfaces, fine feature reproduction, growing resin range covering rigid, tough, flexible, and high-temperature grades Limits: photopolymers are more brittle and less UV-stable than engineering thermoplastics, parts need washing and a UV post-cure, resin handling requires gloves and ventilation Best for: master patterns for casting, enclosures with tight tolerances, optical and lens prototypes, consumer-product appearance models DLP projects a full layer image at once, so build time depends on part height rather than cross-sectional area. That makes it faster than laser-scanned SLA for trays of small parts. Both processes depend on a controlled post-cure to reach final mechanical properties, which is where a dedicated lamp or chamber matters more than the printer itself. See the best UV lamp for resin curing for matching output to resin chemistry. Selective laser sintering Strengths: no support structures, near-isotropic strength, functional nylon parts, nested builds for volume Limits: grainy matte surface, powder handling and sieving, higher machine cost, 0.3 mm minimum wall Best for: functional end-use components, ducting and manifolds, low-volume production bridge parts, aerospace and industrial brackets PolyJet Strengths: multi-material and multi-color in one build, 16 to 30 micron layers, rigid and rubber-like zones in the same part Limits: high consumable cost, smaller build volume, photopolymer aging under UV Best for: overmold and gasket prototypes, tactile design review models, complex assemblies printed as one piece Email Us to discuss adhesives and coatings that bond or protect printed photopolymer parts. Matching the process to the project Four questions narrow the field quickly: Does the part carry load, or only communicate geometry? Load-bearing points to SLS or filled FDM. How fine are the smallest features and how smooth must the surface be? Sub-millimeter detail points to SLA, DLP, or PolyJet. What is the service temperature and UV exposure? Photopolymers soften and yellow sooner than sintered nylon or ABS. How many units, and how fast? Nested SLS or DLP trays beat single-head FDM for batches. Tolerances and material properties by process Dimensional accuracy and mechanical behavior vary widely: FDM holds roughly plus or…