FDM vs Resin: Which Do You Need?

1. Melting vs curing

FDM works thermally. A spool of solid thermoplastic — PLA, PETG, ABS, nylon — is heated past the point where it flows, and pushed as a fine bead through a nozzle. Each bead cools and welds to the one below it.

Resin printing works chemically. A vat with a transparent base holds liquid resin: monomers plus a photoinitiator. Below the vat, an LCD panel masks a UV light source so that light reaches only the areas that should be solid. Wherever the light lands, the liquid cross-links and hardens.

That difference explains almost everything else about the two processes.

2. Layer lines and surface finish

Because FDM lays down rounded beads, the boundary between layers leaves a fine ridge — layer lines, sometimes called stair-stepping. Thinner layers reduce them, but the texture stays detectable by touch. Sanding, filling or coating removes them if the finish matters.

Resin has no bead. The liquid flows around fine features before it cures, so the part comes out of the wash with a smooth surface and layer transitions that are difficult to see. This is the single biggest practical difference between the two.

3. Strength and direction

FDM parts are anisotropic: they are stronger along the direction the filament was laid down than across the bond between layers. Print orientation is therefore a real design decision, not an afterthought. Engineering filaments such as PETG, ABS and fibre-filled grades give considerable toughness within that constraint.

Resin parts are closer to isotropic, because the chemical cross-linking carries across layer boundaries as it cures. Standard resins can be brittle under a sharp impact; tough and engineering-grade formulations trade some detail for more give.

4. Colour

FDM can change filament during a print, which is what makes multi-colour work possible: colour is built into the part rather than painted onto it, so it cannot scratch or peel off. MetaFuse3D prints up to 16 colours in a single print.

Resin printing uses one resin per vat. A multi-colour resin object has to be printed as separate parts and assembled, or painted after the fact.

5. Choosing

Choose FDM when the part is large, has to take load or impact, will live outdoors, or wants colour built in.

Choose resin when the part is detail-led: fine features, a smooth surface straight off the machine, dental and orthodontic work, jewellery patterns, or masters for casting.

When a part wants both, splitting it is usually cheaper than compromising on either.