SLS vs MJF: Which Nylon Process Actually Fits Your Project?

The Hard Numbers: How They Actually Differ

Dimension                         /             SLS                      /              MJF                                   /          Winner For

Surface texture   /Grainy, powdery (typical finish) / Smooth, dense (factory finish)    /    Appearance: MJF

Dimensional accuracy  /±0.3% or ±0.3mm            /    ±0.5% or ±0.5mm                       /     Tight tolerances 

                                      (better on larger parts)       /  (more consistent across sizes)    /     under 100mm: SLS

Wall thickness minimum  /0.6mm (reliable);          /              0.7mm (reliable);              /          Thin-wall 

                                           / 0.4mm (risky)                   /      0.5mm (marginal)                    /      design: SLS

Single part cost             /   Higher                           /             Lower                                 /        One-off

                             / ($15–$40 per part typical)       /           ($8–$25 per part)                /        prototypes: MJF

Batch of 20–50 parts/  Cost drops 20–30%         /         Cost drops 10–15%                /      Small batches: SLS

Dyeing/coloring      / Accepts color well,              /      Accepts color, but slight             /       Color consistency: 

                               /  consistent dye uptake          /   surface inconsistency can show      /               SLS

Mechanical strength  / Slightly higher                                Excellent                                    /     Repeated impact

                            / (better fatigue resistance)     /    (post-cure improves further)           /              /flex: SLS

Production time  /  5–7 days typical                    /              3–5 days typical                 /          Speed: MJF

Complex/undercut  /Handles better                     /        Fine, but requires                    /      Complex shapes: 

geometry          /    (no support needed)              /           careful nesting                       /                SLS

Quick read: Pick SLS for durability, color, and batches under 50 parts. Pick MJF for speed, smooth finish, and tight tolerances on medium-sized parts.

Where Each One Actually Shines: Real Application Scenarios

Mechanical snap-fits and hinges → SLS

When your part flexes thousands of times, fatigue becomes the enemy. SLS has a slight edge in fatigue resistance. A hinge printed in SLS survives 50,000+ open-close cycles reliably. MJF hits 30,000–40,000 before cracking starts. That difference matters if your product lives in a user's hands every day.

The grainy surface of SLS isn't a bug here—it's slightly self-lubricating, which actually helps mechanical components move smoothly.

Wearable brackets and connectors → Either, depends on use

Outdoor gear, straps, harness connectors—anything that takes abrasion and impacts. Both materials handle this, but SLS wins if the part is being dyed (outdoor orange, tactical black). MJF wins if you need the connector to lock precisely into another component (smooth surface, tighter tolerances).

Enclosure shells and housings → MJF

If you're printing a protective case or equipment housing, MJF's smooth surface is immediately obvious. It looks finished. Sand and paint optional (though still common). Print one, and it looks professionally made. SLS requires post-processing—sand, prime, paint—to reach similar aesthetics. If appearance matters, MJF saves labor.

Mechanical jigs, fixtures, and production tooling → SLS

Manufacturing support parts, alignment jigs, drill guides—these live in factories. They don't need to look pretty; they need to work reliably for months. SLS handles repeated use, dimensional consistency across batches, and the abuse of a shop environment better. Plus, batching 20–50 pieces drops the per-unit cost dramatically.

Prototypes and first articles → MJF for speed, SLS for iteration

Testing a new design next week? MJF. The 3–5 day turnaround matters more than surface texture. You'll print it, test it, likely redesign it.

But if you're printing five variants to compare, SLS batching economics favor that workflow. You pay less per variant and the faster iteration pays off.

Small-run consumer products and collectibles → SLS

Selling 30 pieces of a custom part to enthusiasts? SLS batch pricing (where each part gets cheaper after the first 5–10) hits your margin differently than MJF's linear scaling. Plus, dyeing nylon in custom colors is easier with SLS—people will actually buy a "titanium blue" version if you offer it.

High-precision mechanical components → Depends on tolerance

Parts under 100mm with tight tolerances? SLS. Parts 100–300mm? MJF has the advantage because its tolerance tightens at mid-scale. Parts over 300mm? SLS again (MJF nesting becomes inefficient).

Design Rules: Making Either Process Work Reliably

Minimum wall thickness:

SLS can handle 0.6mm walls reliably. MJF wants 0.7mm. Below that, you're entering "works sometimes" territory.

For mechanical parts under stress, don't use minimum thickness. Jump to 1.0–1.5mm and add internal ribs. A thin-walled part might print, but it'll fatigue faster and break unpredictably.

Snap-fit and undercut geometry:

SLS is the clear winner for complex undercuts and snap geometry because it doesn't need support material. Print an undercut hook and remove powder. It just works.

MJF prints support material inside any undercut. Removing it is tedious. Design conservatively: avoid severe undercuts, or plan 2–3 hours of hand cleanup per part.

Tolerances for assembly:

Both processes have variation. Design conservatively:

• Holes: size them 0.3mm larger than nominal (MJF) or 0.2mm larger (SLS)

• Shafts: size them 0.3mm smaller than nominal (both)

• Snap-fit engagement: 0.5–1.0mm clearance, never 0.1mm

• Hinge pins: 0.4mm loose fit, not snug

These aren't perfect numbers. They're starting points. Test your tolerances on the first prototype.

Accounting for shrinkage and settling:

Printed nylon shrinks slightly as it cools (1–2% linear). Annealing (controlled heating and cooling) reduces this but doesn't eliminate it. If you need true precision, print the first batch and measure the actual finished dimensions before locking in tolerances for scaling.

Different SLS machines from different vendors can vary slightly. MJF is more standardized across vendors, so if you're scaling across multiple suppliers, MJF brings predictability.

Ribs and reinforcement:

Thin sections fail. Add ribs—internal support beams running perpendicular to stress direction. For SLS, ribs as thin as 0.8mm work. For MJF, go 1.0mm minimum. Space them 20–30mm apart on large sections.

This is where design separates amateur parts from ones that last in the field.

From Sample to Production: Costing and Timing Reality

Single prototypes (1–3 parts):

MJF is cheaper. Maybe $20–$30 per part. SLS wants to process a batch so you're paying "batch overhead" for a single piece ($25–$40).

If you only ever need one, MJF wins. If you know you need ten eventually, bite the bullet and run the SLS batch.

Small batches (10–50 parts):

SLS pricing gets interesting. First part costs $40. Second through tenth drop to $10 each. Parts 11–50 drop to $8 each. Suddenly you're printing 50 for the cost MJF charges for 35.

MJF scales linearly. First part is $20, part 50 is still effectively $20 (slight economy, but minimal).

Medium batches (50–200 parts):

Both become reasonable for small runs. SLS maintains its batch advantage. MJF's smooth finish starts justifying the cost if appearance matters to your customers.

At this scale, think about "rolling" your order. Print 30 first, test market response, then print 50 more. SLS batch pricing supports this workflow beautifully.

Rolling orders and iteration:

The smartest small-scale strategy: print 20–30 SLS parts in month one. Sell them, collect feedback. Print 50 more in month two with minor tweaks. The batch economics reward this approach.

You're not committing to 1,000 units before you know they sell. You're testing and scaling.

Dye consistency across batches:

If you're offering multiple colors, dye in batch. Don't dye 10 in blue, then dye 10 more blue a month later and expect them to match—they won't. Color will drift slightly.

Solution: order all your colored parts dyed at the same time by the same shop. Dyeing facilities do this—take 50 parts in five colors, dye them all in the same vat cycles, they'll match.

If you can't batch dye, accept that color variation exists and maybe embrace it as "hand-finished aesthetic" rather than flaw.

Specific Recommendations by Part Type

Part Type                          /              Process                /                                       Why

Mechanical hinge or snap-fit    /       SLS                   /            Fatigue resistance, no support cleanup

Protective enclosure shell     /          MJF                 /               Smooth finish, tight tolerances, speed

Jig or production tooling          /        SLS                /            Batch economy, durability under repeated use

Consumer product (20–100 units) / SLS              /              Color options, batch pricing, perceived quality

Prototype (1–3 units)             /         MJF                /                      Lower cost for single runs, fast

High-precision bracket        /     Depends: SLS          /                  Accuracy varies by part size

(tight tolerance)      /  if under 100mm, MJF if 100–300mm/

Wearable or outdoor gear     /         SLS                           /       Dye options, fatigue resistance in field

Show/display piece               /         MJF                      /             Pristine finish right off the printer

Before You Decide: Questions Worth Asking

What's the failure mode if this breaks?

Catastrophic (person gets hurt)? Use SLS, larger walls, reinforced ribs. Inconvenient (product stops working)? Either process, but design for easy replacement. Ugly (cosmetic fail)? MJF's finish hides minor imperfections better.

How many times will this be used before replacement?

Tens of times? Either works. Thousands of times? SLS. Millions? Maybe neither—you're looking at true injection molding economics at that scale.

Do you need multiple colors?

SLS with dyeing is the answer. Build inventory in natural nylon, then dye on demand. MJF has limited color options natively—you're mostly stuck with its default appearance.

When do you need it?

Next two weeks? MJF. Next month? SLS (batch pricing makes the 2–3 week longer wait worth it). Ongoing? Either, but plan rolling orders with SLS for cost optimization.

What's your tolerance stack?

Hyper-precise (±0.2mm)? Probably neither PA12—step up to resin or machined metal. Loose (±1.0mm)? Either works. Medium (±0.5mm)? Both can handle it, but SLS is more consistent on smaller parts.

Ordering and Timeline: What Actually Happens

SLS workflow:

You upload CAD. Within 24 hours, you get a quote and production schedule. Printing takes 3–5 days depending on batch size. Cooling/post-processing adds 2 days. Dyeing (if ordered) adds 1–2 days. Total: 5–10 days from approval to your door for a small batch.

MJF workflow:

Upload CAD. Quote within 24 hours. Printing 2–4 days. Post-processing 1 day. Total: 3–6 days door-to-door.

Both timelines assume you're not requesting custom support structure or unusual geometry that requires design review.

Quick Decision Card 

Need it durable and you're printing 10+ parts:
→ SLS, accept textured surface or budget for sanding

Need pristine finish and you're in a hurry:
→ MJF, pay the speed premium

Need multiple colors or batching economy:
→ SLS, order in batches, dye post-process

Need one prototype next week:
→ MJF, move fast, decide later

Ready to Print Your Parts

Have CAD ready and unsure which process? Upload your file with a note about your use case. We'll recommend based on your actual requirements—not what we want to sell you.

Need help deciding during design? Share your part and constraints. We'll model it correctly for whichever process wins, including all the wall thickness and rib reinforcement that makes the difference between "works sometimes" and "actually reliable."

Practical Questions That Come Up

Is MJF actually more expensive?

Not for single parts—it's cheaper. For batches 20+, SLS becomes more economical. The crossover point is usually around 15 parts.

Will thin walls actually break?

Yes. A 0.5mm wall might print, but it'll snap under stress or fail after repeated use. Design 1.0mm minimum for parts under stress, 0.7mm for components with zero dynamic load. Ribs make thin sections viable—use them.

Can I really get consistent dyes across batches?

Not if you're dyeing separately. But if you order 50 parts and specify "20 blue, 20 black, 10 natural" and the dye shop processes them together, consistency is excellent. Separate orders weeks apart? Color will vary visibly.

What about surface finish? Can I paint over it?

Both sand beautifully. Prime, paint, clear coat—standard process. SLS takes paint slightly better because the grainy surface gives mechanical grip. MJF requires lighter sanding before priming.

If I mess up the first batch, can I reorder just the failed parts?

Yes. Reordering is simpler than the first order. You already have approved CAD. If you need 5 replacement parts, that's a quick print. Turnaround is faster.