Why Does MJF Nylon Come Out Grey While SLS Nylon Can Be Dyed Any Color?

It comes down to how the two processes fuse powder. MJF uses a fusing agent printed onto the powder bed and then heat-fused with an energy source, and that agent leaves the finished part a dark grey straight off the machine, inside and out. SLS fuses powder with a laser alone and produces an off-white or cream part with no fusing agent residue, so the surface takes dye evenly.

What's actually happening at the material level

MJF's grey comes from the fusing agent itself, not from the nylon powder. That agent is baked into the part during the fusing step, so it's not a surface coating you can strip off. It's structurally part of how the layer bonded.

Dye a grey MJF part and you're dyeing on top of that base tone, which limits how bright or saturated the result can be. Black works fine over grey. A clean white or pastel doesn't, because you can't lighten a part by adding color to it.

SLS starts from a natural, near-white nylon powder with no fusing agent in the mix. That gives dye a clean base to work from, so SLS parts hold a wider range of colors and typically come out more vivid for the same dye process. This is the main practical reason people reach for SLS over MJF when color matters for the application, not durability.

Does color actually last?

Dye on either process sits in the near-surface porosity of the sintered part rather than penetrating uniformly through the cross-section the way bulk-colored plastic would. Color can wear thin at high-friction contact points on either material, though it's usually more noticeable on SLS parts, precisely because the color shift from white to worn-through is more visually obvious than a grey-on-grey wear spot on MJF.

Neither process should be treated as fade-proof if the part is going to see abrasive contact in service.

What this means for a part spec

If a part is cosmetic and needs a specific, saturated color, plan around SLS nylon rather than MJF. If the part is functional and color is secondary, a bracket, a housing, a jig, MJF's native grey is usually a non-issue, and you're picking between the two processes for other reasons like feature resolution instead.

DigiForge runs both MJF Nylon and SLS Nylon PA12, among other 3D printing materials, with a standard tolerance of ±0.3 mm or ±0.3%, whichever is greater, and a lead time of 5-7 business days. If color is part of the spec, say so up front. It changes which process makes sense before it changes anything about the finishing step.