PLA vs PETG vs PP vs TPU: which filament for your mold?
PLA for cold pours, PETG for hot wax and resin, PP if you hate release agents, TPU for flexible demolding. If you only stock one spool for molds, make it PETG, it handles every common casting material short of high-exotherm resins.
Pick by what you pour
The pour temperature and release behavior of your casting material decide the filament, not the other way around. Match here first, then read the details below.
| You're casting | Print the mold in | Why |
|---|---|---|
| Candle wax (poured 65–85 °C) | PETG | Pour temps sit at or above PLA's ~60 °C soft point |
| Plaster, jesmonite, concrete | PETG | Shrugs off the moisture and alkalinity of wet mixes |
| Epoxy / PU resin | PETG or PP | Exotherm can spike; PP also releases without spray |
| Cold-pour resin, test pieces | PLA | Cheapest and easiest, fine below 60 °C |
| Shapes with mild undercuts | TPU | Flexes off the cast like a silicone mold |
| High-run, zero release agent | PP | Almost nothing bonds to polypropylene |
Head-to-head specs
| PLA | PETG | PP | TPU | |
|---|---|---|---|---|
| Print difficulty | Easy | Easy–medium | Hard | Medium |
| Heat limit | ~60 °C | ~80 °C | ~100 °C+ | ~80 °C |
| Flexibility | Rigid, brittle | Semi-rigid | Semi-rigid | Rubber-like |
| Moisture resistance | Poor | Good | Excellent | Moderate |
| Chemical resistance | Poor | Good | Excellent | Good |
| Food safe? | No | Conditional | Yes, with conditions | No |
| Cost / kg | $10–20 | $15–25 | $25–45 | $20–35 |
PLA: cheap, easy, cold pours only
PLA is the cheapest, easiest-printing option and holds detail beautifully, but it starts to soften around 60 °C, right where most candle wax pours. It's also brittle and degrades with repeated water exposure.
Use it for test molds, masters, and genuinely cold pours. Typical settings: 190–220 °C nozzle, 40–60 °C bed, no enclosure. It's a fine first material to feed into a generated mold, see how to turn any STL into a mold.
PETG: the mold default
PETG is the workhorse: ~80 °C heat resistance covers candle wax pours, good moisture and chemical resistance covers plaster and soap, and strong layer bonding keeps molds watertight. It's barely harder to print than PLA.
Food safety is conditional: the raw resin is generally food-safe, but layer-line porosity, brass-nozzle contamination and colorants can make a print unsafe. Use certified food-safe PETG ($25–40/kg vs $15–25 standard), a stainless-steel nozzle, and seal layer lines with food-safe epoxy.
PP: nothing sticks to it
Polypropylene's low surface energy means casts release without any release agent, the same property that makes PP impossible to glue. Add the best chemical resistance of any common filament, ~100 °C+ heat tolerance, and natural watertightness, and it's the top direct-print mold material on paper.
The catch: PP warps badly. It needs an enclosure, a PP-specific bed surface (PP tape or Magigoo PP), and 220–270 °C nozzle with an 80–105 °C bed. At $25–45/kg, save it for molds you'll reuse a lot.
TPU: the flexible demold
TPU is the only common filament that's genuinely flexible (Shore 85A soft to 98A firm). A TPU mold peels and flexes off the cast, handling mild undercuts and detailed shapes that would lock solid in a rigid print, a halfway point to a real silicone mold.
It wants a direct-drive extruder and slow speeds (20–30 mm/s), and heat tolerance tops out around 80 °C. Typical settings: 220–240 °C nozzle, 30–60 °C bed, minimal retraction. $20–35/kg; start with 95A.
Filament questions
Is PLA safe for food contact?
No. Standard PLA is porous, usually carries colourants that are not food-contact rated, and degrades under repeated moisture.
The printed part is the problem more than the polymer: layer-line crevices hold residue that no wash reaches. Cast a food-grade silicone from the print instead, see food-safe molds.
Is PETG food safe?
The resin Generally yes.
The printed part Often not. Three separate risks: layer-line porosity, brass-nozzle contamination, and colourants that were never assessed for food contact.
To do it properly Certified food-safe PETG, a stainless or hardened steel nozzle, a clean machine, and a smooth sealed surface. Miss one and the certification on the spool means nothing.
Can I print PETG without a heated bed?
No. PETG needs 70–90 °C on the bed. Without it you get poor adhesion and warping, and a mold that warps is a mold that leaks.
Is PP worth the hassle?
The upside Almost nothing sticks to polypropylene, so you can skip release agents entirely, and it survives hot pours PLA cannot.
The downside It is notoriously hard to get to stick to a bed, and it shrinks.
Verdict Only if you cast often enough that the saved release agent and the extra heat tolerance pay back the printing pain. For occasional molds PETG is easier and close enough.
Which TPU hardness should I buy first?
95A. Flexible enough to peel off a cast, firm enough to print consistently, and versatile across most flexible-mold shapes.
Softer Below about 90A it gets genuinely hard to feed and print reliably, which is a lot of frustration for a little more stretch.
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