Resin Exotherm Heat Calculator

How It Works

Every resin curing reaction releases heat (exothermic reaction). In thin layers, this heat dissipates harmlessly into the air. But as pour thickness and volume increase, the surface-to-volume ratio drops — heat gets trapped inside the casting.

The calculator models three factors that compound risk:

• Thickness ratio — how close your pour is to the resin's known safe limit
• Volume factor — larger masses retain more heat (above 500ml, risk scales significantly)
• Temperature factor — higher ambient temps give the reaction a "head start"

The estimated peak temperature combines all three into a single risk assessment: Safe (green), Caution (yellow), or Danger (red). When layering is recommended, the calculator suggests how many pours you need and how long to wait between them.

How to Use This Calculator

1. Select your resin type — different formulations have vastly different heat profiles. Deep-pour epoxies are engineered for thick castings; standard epoxies are not.
2. Enter pour thickness — the maximum depth of resin in your mold, in millimeters.
3. Enter volume — total amount of mixed resin you plan to pour. Larger volumes are riskier even at the same thickness.
4. Check ambient temperature — if your workshop is above 30°C, consider cooling the space before pouring.
5. Read the assessment — if yellow or red, follow the layering recommendation.

Tips & Safety Notes

• Always do a small test pour first with a new resin brand to observe heat behavior.
• River table molds can exceed 1000ml easily — use only deep-pour formulas rated for your depth.
• If your resin starts smoking or you smell burning, do NOT add water. Move it outside to a non-flammable surface and let it cure.
• Silicone molds tolerate heat better than plastic molds. Wooden molds with thin walls can char.
• In summer, consider pouring in the evening when temperatures drop.
• Fast-cure epoxies (5-minute type) should never be poured in bulk — they are designed for small repairs only.

FAQ

How thick can I pour epoxy resin in one layer?

Standard clear epoxy is typically safe up to 10-12mm per layer. Deep pour formulas (river table epoxy) can handle 40-50mm depending on brand. Always check your specific product's TDS (Technical Data Sheet) for the manufacturer's recommended maximum depth.

What happens if resin gets too hot during curing?

The casting may crack from thermal stress, turn yellow or brown from heat damage, shrink excessively, warp, or in extreme cases produce smoke. Temperatures above 150°C can damage molds and surrounding materials. At 200°C+, some resins can auto-ignite.

Can I cool resin with a fan during curing?

Surface airflow helps slightly but cannot address heat trapped deep inside a thick pour. The most effective strategy is to pour in thin layers and allow each to partially gel before the next. Some artists place molds in a water bath for very large castings.

Does mixing ratio affect exotherm risk?

Yes. Adding excess hardener accelerates the reaction and increases peak temperature. Always measure precisely. Over-catalyzed polyester resin is particularly dangerous and can reach ignition temperatures within minutes.

Related Tools

• Epoxy Resin Ratio Calculator — Calculate precise Part A and Part B weights for mixing
• Candle Wax & Fragrance Calculator — Another heat-sensitive crafting calculation

Last reviewed: June 2026