Both modes make the same kind of thing, a printed housing you pour liquid silicone into around your master. They differ in how much silicone that takes and how much work the printed part is.
| Box mold | Contoured shell | |
|---|---|---|
| Shape | A rigid rectangular or round box | Follows the master's real silhouette |
| Silicone used | Fills the whole volume around the master | Considerably less on anything not roughly cuboid |
| Printed parts | Few, simple | A multi-part shell that clips together |
| Best for | Compact, blocky masters, and a first mold | Tall, thin or branching masters, and expensive silicone |
| Fiddliness | Low | Higher: more seams to seal, more to align |
The short version: a box mold is easier and a contoured shell is cheaper to fill. On a squat, boxy master there is little in it, so start with the box. On a figure, a branch or anything tall and thin, the box wastes most of what you pour and the shell pays for its extra fiddliness on the first cast. Switch between them with the control at the top of the panel; whichever mode is open, the tool estimates the silicone volume before you print anything.
It makes the tooling: the housing or shell, plus a shrink-compensated master positive of your object. It does not make the silicone mold, because that is a physical thing you cast. You never print the flexible part.
You print the housing, seal your master inside it, then mix and pour a liquid two-part rubber around it. Once it cures you peel the housing off, and the flexible block left behind is your reusable mold. That flexibility is the whole point: it releases undercuts a rigid printed mold physically cannot.
A platinum-cure (addition) silicone around 20 to 30 Shore A covers most resin, soap and wax casting. Softer than that tears on demolding; harder than that stops releasing undercuts, which is the reason you are using silicone at all. Degas it or pressure-cast if you need reliably bubble-free results, though the pouring technique below gets you most of the way without either. The full walkthrough is in the silicone mold guide, and the silicone calculator turns a volume into a cost.
| Setting | Use | Why |
|---|---|---|
| Material | PLA is fine | Silicone cures at room temperature, so there is no heat to resist |
| Walls | 3 to 4 perimeters | The part has to hold a column of liquid without bowing |
| Infill | 15 to 20% | Perimeters carry the load; infill only stops flex |
| Layer height | 0.2 mm | The housing's own finish never reaches the cast |
| Seams | Tape or hot glue, on the outside | Uncured silicone finds every gap, and one leak wastes the whole pour |
A contoured shell has more seams than a box by definition, so budget a few more minutes for sealing it.
Meshcast prints a rigid housing or a form-hugging shell plus a master positive of your object. You print those, seal your master inside, then mix and pour casting silicone around it. Once cured you peel the housing or shell off, leaving a reusable flexible silicone mold.
You print the housing (or shell) and master. The silicone itself is poured as a liquid two-part rubber and cures inside the printed part, so you never print the flexible part.
A platinum-cure (addition) silicone in roughly 20-30 Shore A works for most resin and soap casting. Degas or pressure-cast if you need bubble-free results. See our silicone mold guide for the full walkthrough.
The housing or shell: the rigid printed part you pour liquid silicone into around your master. The silicone mold itself is the physical thing you cast in it, then peel the housing off.
The box mold pours into a rigid rectangular or round housing and fills the whole volume around your master. The contoured shell hugs the master's true silhouette instead, which uses considerably less silicone on anything that is not roughly cuboid, at the cost of a more involved multi-part clip-together shell.
The tool estimates the volume before you print anything, which is worth checking first because silicone is the expensive part of the job. A box mold fills the whole volume around the master, so the contoured shell uses considerably less on anything that is not roughly cuboid.
Cure inhibition: something on the master shut down the platinum catalyst. Resin-printed masters that have not been fully washed and post-cured are the most common cause. Sulfur-containing clay, latex gloves and superglue residue do the same.
PLA is fine. Silicone cures at room temperature so there is no heat to resist. Use 3 to 4 perimeters so it does not bow under a column of liquid, and seal the seams from the outside.
Stir slowly with the stick kept below the surface, then pour a thin stream from a height so bubbles break on the way down, and brush a first coat into fine detail before pouring the bulk. Technique gets you most of the way there.
Silicone is denser than most printed masters. Glue it down with a dab of hot glue or double-sided tape before pouring.
Uncured silicone is thinner than people expect and finds every seam. Seal the outside of every joint with tape or hot glue before pouring, and stand the whole thing in a tray so a leak costs you silicone rather than your table.