Silicone mold or direct-print mold?
Direct-print when you want a mold today, the shape is simple, or dimensions must be exact, €1–3 of filament, casting the same day. Silicone (poured over a printed master) when you need undercuts, a glossy cast surface, hot pours, or 50+ casts from one mold.
The 60-second decision table
| Situation | Best approach |
|---|---|
| Testing a new shape quickly | Direct-print |
| Production run of a proven design | Silicone |
| Flat or geometric cavity (soap bars, tiles, trays) | Direct-print |
| Complex 3D shape with undercuts | Silicone |
| Hot pours (wax, soap batter) | Silicone, or PETG/PP direct-print, check pour temp |
| Cold-pour resin | Either, direct-print if flat, silicone if detailed |
| Glossy cast surface needed | Silicone |
| Exact dimensional repeatability | Direct-print |
| Custom one-off designs | Direct-print |
| Tight budget | Direct-print |
| Scaling a popular SKU | Silicone |
The five criteria that decide it
| Criterion | Direct-print | Silicone |
|---|---|---|
| Cost to first cast | €1–3 (50–150 g filament) | €15–40 silicone + master; good silicone runs €30–80/kg |
| Time to first cast | Same day | Print master + 4–24 h silicone cure |
| Durability | Reprint anytime, the file is the mold | 50–100 uses (wax/soap), 20–50 (resin) |
| Detail & surface | Layer lines transfer to the cast | Naturally smooth, captures fine texture faithfully |
| Heat | PLA ~60 °C, PETG ~80 °C, PP more | 200–250 °C continuous |
| Food safety | Conditional, needs certified filament + sealing | Food-grade silicones readily available |
When the $5 PLA mold wins
Direct-print molds have near-zero setup: model the cavity (or generate it from an STL), print, pour the same day. Cheap enough to print five versions and bin four.
- Prototyping. No silicone wasted on a shape that might not work.
- Exact dimensions. Rigid prints don't stretch during demolding the way silicone does on tall walls, better for parts that must fit together.
- Flat and low-relief shapes. Trays, bars, tiles: no undercuts, easy demolding, layer lines barely matter.
When silicone wins
Silicone flexes off the cast, so it releases undercuts, re-entrant curves and fine texture that mechanically lock a rigid mold. The cavity is naturally smooth and non-stick, the mold does the surface finishing for you.
It also laughs at heat (200–250 °C continuous) and lasts a production run: 50–100 casts for wax and soap, 20–50 for resin. Platinum-cure outlasts tin-cure and is worth the premium for repeat work. For food-contact casting, food-grade silicone is the clean answer, see food-safety basics.
The downsides: 4–24 h cure before first use, real material cost, and a workflow (accurate mix ratios, bubble management, support housings for tall molds) that takes practice.
The smart workflow: use both
- 1. Validate with a direct print. Test geometry, fill and demolding for €2 before committing silicone. Then run your first cast.
- 2. Lock the design, cast it in silicone. The silicone mold becomes the production tool; your printer moves on to the next job.
- 3. Keep the master as a file. Reprint it anytime to cast a fresh silicone mold when the old one wears out.
Deciding between them
Can I pour silicone directly into a 3D print?
Yes, and it is the workflow most people should use. Print a rigid housing, pour liquid silicone into the cavity, cure, and peel.
What you get A flexible silicone mold with printed-mold precision: the detail comes from the printed master, the release comes from the silicone.
The silicone mold generator builds the housing for you.
Can I use PLA for candle molds?
Yes, with a caveat that is usually stated backwards.
The numbers PLA softens from around 60 °C. Most candle wax pours at 65–85 °C, so the wax IS hotter than the plastic likes. It works because the wax mass is small, the contact is brief and the wall is thick.
Safer Pour at the low end of your wax’s range, keep 4 walls, and use PETG if you pour hot regularly.
How many casts will a silicone mold survive?
Candle and soap 50–100 pours.
Resin 20–50, because the exotherm and the release agents attack the surface far faster.
Platinum-cure significantly outlasts tin-cure at both, and it is worth the extra cost the moment you are casting to sell.
What is the cheapest way to start?
Step 1 Direct-print PETG molds, to test whether the design is any good. Filament is cheap and iteration is fast.
Step 2 Once a shape actually sells, buy 500 g to 1 kg of platinum-cure silicone and cast a production mold from your printed master.
Doing it in that order means you only ever buy silicone for designs that have already earned it.
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