Everything here runs on a Formlabs Form 4, so resin is what we print. That means this page has an obvious bias, and the honest thing is to name it up front and then tell you the truth anyway: for a real share of parts, filament is the better answer, and we would rather say so than take a job that ends in a part you are quietly disappointed by.

The actual difference

FDM builds a part by pushing melted plastic through a nozzle and drawing each layer as a path. The nozzle has a width, so the smallest feature it can make is roughly that width, and every layer leaves a visible ridge.

SLA builds a part by curing liquid resin with light. There is no nozzle and no path — an entire layer forms at once, at whatever resolution the optics can project. At 25 microns the layers stop reading as layers.

That single difference drives almost everything below.

Where filament wins

Size. FDM machines are routinely far larger than resin ones, and material is cheap by volume. A big part is a big part.
Toughness. Common filaments bend before they break. Many resins are stiffer and more brittle by comparison, so a part that gets dropped, flexed, or clamped often does better in filament.
Cost on bulk geometry. If the part is mostly volume and the surface does not have to be beautiful, you are paying resin prices for something filament could do.
Heat and outdoor use. Standard resin parts are not the right call for a hot car dashboard or long sun exposure.

If your part is a large bracket that has to survive being stood on, that is a filament part. Ask us and we will tell you the same thing.

Where resin wins

Detail. Faces, fabric folds, engraved text, filigree, rivets. Features measured in tenths of a millimeter survive.
Surface. Parts come off smooth enough to prime and paint without sanding layer lines out first, which is most of the work on a filament miniature.
Small parts. Below a certain size, a nozzle simply cannot draw the shape.
Casting patterns. Castable resin burns out clean for jewelry casting. Filament does not do this job at all — see castable resin vs. hand-carved wax.
Clarity. Clear resin can be finished to genuine transparency. Clear filament is translucent at best.

The quick test

Ask what the part is for.

If somebody is going to look closely at it — a miniature, a bust, a display model, a presentation piece, a pattern for casting — the surface is the product, and that is resin. If somebody is going to use it, load it, or never really look at it, filament is probably enough and probably cheaper.

Prototypes fall on both sides. An appearance model for a client meeting is resin. A fit-check for something that bolts to a machine is usually filament, unless the fit depends on features too fine to print any other way.

Seeing it side by side

There is a photograph in our recent work of the same model printed both ways, shot under the same light. It is the fastest version of this entire article. The filament print is not bad — it is doing exactly what filament does — but at that scale the difference is not subtle.

If you are still not sure

Call (239) 880-2698 and describe the part. It takes about a minute to work out which process it wants, and the answer is free either way. Quotes are free, prints start at $29, and shipping is free anywhere in the USA — details on the pricing page.

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