FDM and SLA at a glance
FDM (Fused Deposition Modeling) and SLA (stereolithography) are the two most widely used plastic 3D printing technologies. Both build a part layer by layer, but from a completely different starting material: FDM melts a strand of filament, SLA cures a liquid resin with light.
The upshot: FDM is affordable and suits larger, simpler parts where looks matter less. SLA costs a little more per cm³, but delivers fine detail, crisp edges and a smooth surface that is almost presentable straight away.
FDM vs SLA comparison table
| Feature | FDM | SLA |
|---|---|---|
| Raw material | Plastic filament | Liquid photopolymer resin |
| Layer height | 0.1-0.3 mm | 0.01-0.2 mm |
| Surface | Visible layer lines | Smooth, fine detail |
| Strength | Tough, but weaker between layers | Uniform, standard resins rather brittle |
| Materials | PLA, PETG, ABS | Grey, White, Black and Clear Resin |
| Transparent possible | No | Yes, with Clear Resin |
| Price from | €0.15/cm³ | €0.20/cm³ |
| Where | In-house | In-house |
All prices are starting prices per cm³, excl. VAT and excl. finishing.
How does FDM work?
In FDM, a plastic filament is fed through a heated nozzle. The print head moves over the build plate and deposits the molten material as a thin bead. Once a layer is done, the plate steps along and the next layer follows. Overhangs get temporary supports that are removed afterwards.
Because each layer is a rounded bead, you can see and feel the layer lines. With layer heights of 0.1 to 0.3 mm that's no problem on larger parts, but small details and sharp corners come out less crisp than with SLA.
How does SLA work?
In SLA, the build platform sits in a tank of liquid resin. A light source cures exactly the cross-section of the part, layer after layer, with layers down to 0.01 mm. After printing, the part is washed, post-cured under UV light and its supports are removed.
The result is a smooth, closed surface with crisp edges and fine detail, with a tolerance down to ±0.1 mm. At Makernaut an SLA part can be up to 780 × 780 × 530 mm.
Layer lines or a smooth surface
The most visible difference between FDM and SLA is the surface. An FDM print has a clear ribbed texture, especially on sloped and curved faces. That's fine for a jig, a fixture or a concept model, less so for a presentation model or a part that should resemble the future injection-moulded product.
An SLA print already feels smooth when it comes off the printer. With sanding, primer and paint it becomes a model that is hard to tell apart from a finished product. We do that finishing in-house too.
Strength: which is stronger, FDM or SLA?
It depends on direction and material. An FDM part in PETG or ABS is tough and can take a knock, but the bond between layers is the weak spot: pull at right angles to the layers and the part breaks sooner. So choose the print orientation so the load runs along the layers.
SLA parts are more uniform in every direction and stiff, but standard resins such as Grey and Clear Resin are rather brittle. They're ideal for checking form and fit, less so for snap-fits or parts that need to absorb impacts.
Materials and starting prices
| Material | Technology | Typical use | From |
|---|---|---|---|
| PLA | FDM | Concept models, early prototypes | €0.15/cm³ |
| PETG | FDM | Mechanical parts, jigs, fixtures | €0.35/cm³ |
| ABS | FDM | Functional parts, enclosures | €0.32/cm³ |
| Grey Resin | SLA | General prototypes, fit models | €0.45/cm³ |
| Clear Resin | SLA | Transparent parts | €0.50/cm³ |
Worked example
A part with a volume of 50 cm³ costs from €7.50 in PLA and from €22.50 in Grey Resin, per part and excl. VAT. Volume times material price is a starting point: your actual SLA price is shown in Quotebase, and for FDM you get a custom quote.
When should you choose FDM?
- You want the lowest price per part and looks are secondary.
- You're making a concept model to judge shape and size.
- You need jigs, fixtures or holders for the shop floor.
- The part is large and simple in shape.
- You want a tough material such as PETG or ABS for a functional test.
When should you choose SLA?
- You have fine details, small text or thin ribs.
- The part must look smooth and polished, e.g. for a presentation or photo shoot.
- You're checking fit and dimensions of small parts.
- You want a transparent part in Clear Resin.
- You need a master pattern for vacuum casting.
Not sure? Many projects use both: a first version in FDM to test the shape, then an SLA version to judge detail and appearance. For SLA you calculate your price straight away in Quotebase. FDM isn't in Quotebase yet: request a custom quote at info@makernaut.be and you'll get an answer within one working day.