Which mold to print: silicone box vs two-part vs plaster

The right mold to print depends on what you're casting and the shape of the part. In short: print a silicone box mold for detailed, flexible, reusable molds (resin, concrete, soap); print a two-part box mold to cast simpler rigid parts like wax, candles, and soap directly; and print a plaster slip-casting mold for ceramics. Here's how the three differ and how to choose.

The quick answer

• Silicone box mold → you print a box, pour silicone into it, and cast in the flexible silicone. Best for fine detail, undercuts, and reuse.
• Two-part box mold → you print a rigid two-half mold and cast directly into the plastic. Best for simple shapes and materials like wax, candles, and soap.
• Plaster slip-casting mold → you print a box, pour plaster, and slip-cast liquid clay in the plaster. Made specifically for ceramics.

Silicone box mold

With a silicone box mold, the print isn't your mold — it's a form you pour silicone into. The flexible silicone that comes out is the real mold, and it's the most versatile option: it captures crisp detail, flexes to release undercuts without breaking the cast, and lasts for many pours. It's the go-to for resin, concrete, and soap, and anything with texture or complex geometry. The trade-off is the extra step and the cost of the silicone. See how to 3D print a silicone mold box to get started.

Two-part box mold

A two-part box mold is the direct route: you print a rigid mold in two halves with alignment keys and a pour spout, then cast straight into the printed plastic — no silicone in between. That makes it fast and cheap, and it suits wax, candles, and soap, plus simpler resin pieces. Because the mold is rigid, it works best on shapes that can pull apart cleanly along a seam — deep undercuts are hard to release. The generator's tongue-and-groove keys seal liquids best, while pins suit simpler rigid casts.

Plaster slip-casting mold

A plaster slip-casting mold is a specialist. You print a box, pour plaster into it to make the mold, and then slip-cast with liquid clay. Plaster's superpower is that it absorbs water from the clay slip, drawing a solid clay skin against the mold wall — that's exactly how traditional ceramic slip casting works. Choose it when your end material is ceramic; it isn't the tool for resin or wax.

How to choose

Start with your casting material, then check the shape:

• Resin, concrete, or soap with detail or undercuts: silicone box mold.
• Wax, candles, or simple soap you want to cast quickly: two-part box mold.
• Ceramic / liquid clay: plaster slip-casting mold.
• Shape check: deep undercuts and fine texture favor flexible silicone; clean, draftable shapes are fine in a rigid two-part mold.
• Reuse: silicone lasts many pours and releases easily; rigid molds are cheaper but fussier to demold on complex parts.

FAQ

What's the most versatile mold to print?

The silicone box mold. Because you cast in flexible silicone, it handles the widest range of materials, the most detail, and undercuts that would lock up a rigid mold.

Silicone box or two-part — I want to cast resin?

Both can work. Use a two-part printed mold for a simple, draftable shape and a quick result; use a silicone box mold for fine detail, undercuts, or a mold you'll reuse many times.

Why would I use a plaster mold?

For slip casting ceramics. Plaster absorbs water from liquid clay to form the piece — a rigid or silicone mold can't do that, so plaster is the right pick for clay.