Two ways to make a mold
- Two-part mold – a printed block with the model's shape inside, split into two halves that lock together with registration keys. Pour resin, plaster, wax, concrete or soap straight in. Best for simple shapes without deep undercuts.
- Silicone mold box – walls around your model on a base. Pour silicone over the model, let it cure, cut it open and you have a flexible silicone mold that releases even complex shapes. The tool tells you how much silicone to mix.
How to make a two-part mold from an STL
- Drop your model into the box above (STL, OBJ, 3MF or STEP – it must be watertight).
- Set the wall thickness and drag the parting line to the widest part of the model – the halves must pull away without catching.
- Keep the pour hole and air vents: they are placed automatically at the highest points of the model, where air would otherwise get trapped.
- Download both halves, print them flat side down, and clamp them together for casting.
Printing and casting tips
| Setting | Recommendation |
|---|---|
| Layer height | 0.12–0.16 mm for a smooth cavity |
| Walls / infill | 4 walls, 20–30 % infill |
| Release agent | Mold release spray or petroleum jelly on every surface |
| Resin casting | Seal the cavity with a thin coat of epoxy or clear lacquer first |
| Silicone in a printed mold | Use platinum silicone with PLA/PETG; avoid sulfur-containing clays |
How much silicone do I need?
In mold box mode the volume is the inside of the box up to the silicone level, minus the model. Add about 10 % for losses in the cup. Most platinum silicones weigh about 1.1 g per ml, so the tool shows grams too – ready for your scale.
Food safety: FDM prints have tiny gaps where bacteria can grow. For chocolate or ice, use the printed mold as a master for a food-grade silicone mold instead of using the print directly.
Frequently asked questions
Can I make a silicone mold from an STL?
Yes. Use the silicone mold box mode: print the box (with the model attached to the floor), pour silicone, demold. Or print a two-part mold and cast silicone into it for a silicone copy of the object.
Where should the parting line be?
At the widest point of the model, so both halves release without undercuts. Drag the slider and watch the preview.
Why does it say my model is not watertight?
A mold needs a closed solid. Fix holes with the STL repair tool first.
Is it free?
Yes – up to 5 mold downloads a day free, unlimited with Pro.
Is my model uploaded?
No. The mold is built in your browser; the file never leaves your device.