Silicone Moulds from a 3D Printed Jig: The Complete Guide

A flexible silicone mould is the difference between hobby casts and shop-quality product — no layer lines, effortless release, hundreds of pours. The usual barrier is tooling: you need a formwork to pour the silicone into. Our free Mould Maker now generates that tooling — a silicone casting jig — for any shape and size, as a print-ready STL.

How the jig works

The jig has four printed parts: an outer shell with a threaded collar, a core in the shape of your final casting with a threaded spigot, a bridge bar that screws down the spigot, and a clamp ring that screws onto the collar and locks the bar to the rim — suspending the core dead-centre, mechanically locked against the buoyancy of the liquid silicone. Pour mixed silicone into the gap between them; when it cures you own a flexible mould of your shape.

1. Print all four parts flat as exported — no supports needed. 0.12-0.16mm layers give the silicone (and every future cast) a smooth face. PLA is fine; the silicone cures at room temperature. Selling the casts? Sand the core to ~1200 grit and give it one coat of filler primer — every mould poured off it inherits that glass finish. Silk PLA also prints noticeably smoother if you want to skip sanding.
2. Tape the two vent holes — one in the shell base, one through the core. Quality tape, pressed flat.
3. Mix silicone by weight to its exact ratio (digital scales, not eyeballed cups). The designer tells you how many grams to mix for your jig, margin included.
4. Pour a thin stream from high up into one point of the gap and let it flood around. The stretched stream pops most bubbles; tap the jig on the bench to settle the rest.
5. Stop at the core's top face — that level becomes the mould's opening.
6. Cure, then release: peel both tapes and give each vent a short blast from a ball pump or air line. The core lifts out and the finished silicone mould pops from the shell.

Choosing your silicone

• Candles, soap, resin (fine detail): 20A — in Australia that's Barnes Pinkysil (platinum-cure, demould in ~30 minutes) or SiliCreate TC20 (tin-cure, cheaper). Expect $40-60/kg.
• Concrete, jesmonite, plaster: go firmer — 25-30A — so the mould wall doesn't bulge under the slurry's weight. The designer also widens the silicone wall automatically as your piece gets bigger for the same reason.
• Chocolate and ice: use a food-grade platinum silicone — this jig workflow is exactly how food-safe moulds are made from 3D prints, because the print never touches your food.
• Good to know: tin-cure silicone cures against anything. Platinum-cure gives a longer-lived, zero-shrink mould but can refuse to cure against uncured SLA resin prints — irrelevant here, since our jigs are FDM-printed PLA/PETG.

Casting into your new mould

Wax pours at candle temperature straight in — silicone shrugs off 80°C. Soap and plaster are cold and easy. For resin, a light release spray extends mould life. For concrete vessels, cast with the mould supported in its shell so the walls stay true, and demould the next day.

Frequently asked questions