Best print settings for 3D-printed molds
A mold is not a normal print. It has to hold liquid without weeping, keep its dimensions while material sets against it, and leave a surface you are happy to see on every cast. The default profile that prints a great desk toy will quietly fail at all three. The good news is that the changes are small and consistent: a few more walls, slightly thinner layers, a touch more heat, and a sensible orientation. This guide walks through every setting that matters for a printed mold, why it matters, and how to tune it for the material you are pouring.
The goal: watertight and dimensionally true
Two things make or break a printed mold. The first is that it must not leak. A casting mold spends its working life full of liquid - thin resin, runny plaster slurry, molten wax - and any gap between perimeters or a poorly bonded layer becomes a slow weep that ruins the pour and the part. The second is that it must be dimensionally true: walls thick enough not to bow under the weight and heat of the casting, and a cavity that matches the model so the cast comes out the size you designed.
Both of those come down to one underlying property - layer adhesion. The forces that fight a printed mold are pulling layers apart and finding gaps between extrusion paths. Almost every setting below is really a lever on adhesion and gap-free skin: print a touch hotter, a touch slower on the walls, with enough perimeters that the skin is continuous and strong. Get the mold watertight first; finish quality is the easy part once it holds.
Layer height
For most molds, 0.12 to 0.16 mm is the sweet spot. Thinner layers do three useful things at once: they bond more reliably (more contact passes over the same height), they leak less because there are fewer, smaller gaps for liquid to find, and they leave finer layer lines that transfer as a smoother surface onto the cast. The trade-off is print time, which roughly doubles going from 0.2 to 0.1 mm.
0.2 mm is perfectly fine for simple, shallow molds - a coaster blank, a flat-bottomed dish - where speed matters more than a glassy finish and the liquid column is short. Reserve the very fine heights (0.08 to 0.1 mm) for molds where the cast surface is the whole point and you do not want to post-process. As a rule, the deeper the mold and the thinner the liquid, the more a small layer height earns its extra time.
Walls / perimeters
This is the single most important setting for a leak-proof mold, and it matters more than infill. The perimeters are the continuous skin that actually holds the liquid; infill only braces them. Use three walls minimum, and four for deeper molds or any tall column of liquid that puts hydrostatic pressure on the wall. With one or two perimeters, a single gap or a weakly bonded layer line goes straight through to the outside and weeps. Three or four overlapping perimeters give the liquid no continuous path out, even if one bead has a flaw.
Extra walls also stiffen the mold so it does not bow while plaster or concrete cures against it, which keeps the cast dimensionally true. If your slicer lets you set a minimum wall thickness in millimetres, aim for at least 1.2 mm of solid perimeter (three passes of a 0.4 mm nozzle).
Infill & top/bottom layers
Once the walls are doing the watertight work, infill is just structural support so the mold body does not flex. 15 to 20 percent gyroid is plenty - gyroid braces in every direction and is less likely to telegraph a flat-spot pattern through thin walls than a grid. Going higher wastes filament and time without making the mold hold liquid any better.
The base is where many molds quietly fail, so treat it like a wall. Use 5 to 6 solid bottom layers so the floor does not weep where the liquid sits longest and presses hardest. Small molds are the exception - if the part is little, just set infill to 100 percent and make the whole thing solid; it prints quickly, never leaks, and resists heat better. Top layers matter less for an open mold, but keep them solid wherever a face will be in contact with the casting.
Temperature & flow
Printing a few degrees hotter than your normal profile is the easiest watertightness upgrade there is. More heat means each layer fuses more completely into the one below, so there are no micro-gaps between layers for thin liquid to seep through. As a starting point, run PETG around 235 to 245 °C and PLA around 205 to 215 °C - the upper end of each material's range rather than the lowest temperature that "works".
A small flow (extrusion multiplier) bump of one to three percent also helps seal a mold, by slightly over-filling the gaps between adjacent extrusion paths so the skin is truly solid. Do not overdo it - too much flow causes blobs and dimensional drift. Calibrate flow on a test cube first, then add the small bump for molds specifically.
Speed, cooling & ironing
Slow the outer wall down. Printing the external and cavity perimeters at a reduced speed (say 25 to 35 mm/s) lays a cleaner, more consistent bead, which means a better seal and a smoother cast surface. The infill can run fast; it is the perimeters that hold the liquid, so spend the time there.
Cooling is material-dependent. PLA likes plenty of part cooling, but reduce cooling on PETG - too much fan makes PETG layers bond poorly, which is exactly the gap that lets a mold leak. Run the PETG fan low (around 20 to 40 percent) for stronger inter-layer adhesion.
If your slicer supports ironing, ironing the top face of the cavity gives a noticeably smoother surface there, which transfers to a cleaner cast. It only helps flat upward-facing surfaces, so it pairs naturally with orienting the cavity to face up.
Orientation & the parting line
Orientation decides where your weakest seams and your roughest surfaces land. Where you can, orient the mold so the cavity faces up: that puts the detailed casting surface on top where layer lines are finest and ironing can smooth it, and it usually lets the cavity print without supports.
Keep the sealing face flat on the build plate. For a two-part mold, the parting faces need to mate tightly so liquid does not escape at the seam - printing them flat against the plate gives the flattest, most consistent surface to seal against. Finally, position the print so the seam (the slicer's layer start point) does not run down a sealing surface or a visible cavity wall; tuck it onto an outside edge where a tiny scar does no harm.
Supports
Avoid supports inside the cavity at all costs. Support interfaces leave a rough, pocked texture that prints directly onto the cast, and they are nearly impossible to remove cleanly from a concave surface. The fix is geometry, not supports: add draft angles so overhangs become printable and the cast releases, and orient the part so the cavity is self-supporting. See draft angles & undercuts for how much taper to add and how to spot the undercuts that force supports in the first place. Supports on the outside of the mold body are fine if you genuinely need them - just keep them off any surface the casting will touch.
Settings at a glance, per casting material
These are sensible starting points - tune from here for your printer and the depth of your specific mold.
| Casting material | Layer height | Walls | Recommended filament |
|---|---|---|---|
| Plaster / jesmonite | 0.16 mm | 3 | PETG (water-tolerant, easy release with oil) |
| Epoxy / polyurethane resin | 0.12 mm | 4 | PETG or PP - thin resin finds every gap, so fine layers and extra walls |
| Candle wax | 0.2 mm | 3 | PETG - tolerates the warm pour better than PLA |
| Concrete / cement | 0.2 mm | 4 | PETG - tough enough for the weight and abrasion of a thick pour |
FAQ
How many walls for a watertight mold?
Use at least three perimeters, and four for deep molds or a tall column of liquid. Wall count matters far more than infill for leak-proofing, because the perimeters are the continuous skin that actually holds the liquid - a single thin wall almost always weeps through a gap or a poorly bonded layer.
What layer height is best for molds?
0.12 to 0.16 mm is the sweet spot for most molds: thinner layers bond more reliably, leak less, and leave finer layer lines on the cast surface. 0.2 mm is fine for simple, shallow molds where speed matters more than a glassy finish.
Why does my printed mold leak?
Almost always too few walls or weak layer adhesion. Add a perimeter or two, raise the nozzle temperature a few degrees so layers fuse properly, bump flow by a percent or two, and make sure the solid bottom is five or six layers thick. Thin liquids like uncatalysed resin will find any gap a thick paste would bridge.
Do I need supports for a mold?
Avoid supports inside the cavity - they leave marks that print straight onto the cast and are hard to remove cleanly. Design draft angles and orient the part so the cavity prints support-free instead. Supports on the outside of the mold body are harmless if you need them.