Does Silicone Rubber Dry by Exposure to Air or by Mixing?

How Silicone Rubber Hardens

Most silicone rubbers used for mould making are bi-component systems. This means they require you to combine two separate parts, usually in equal proportions (a 1:1 ratio), to trigger a chemical reaction. It’s not the exposure to air, but this chemical process—known as curing—that transforms liquid silicone into a flexible, durable solid.

For instance, “Pure Mould” liquid silicone rubber begins to set shortly after mixing the two parts, typically ready for demoulding within 3 to 8 hours depending on the product and conditions.

Tips for Successful Curing

To achieve the best results, always measure and mix the two components as directed—usually by weight or volume. Stir thoroughly to ensure that the catalytic reaction happens evenly throughout the mixture. Room temperature is generally sufficient for curing; there’s no need for ovens or special environments, although colder spaces may slow down the reaction significantly.

• Use a clean, dry container for mixing.
• Mix slowly to minimise air bubbles.
• Pour the silicone immediately after mixing to capture fine details.

When This Matters

Knowing that silicone rubber cures by mixing, not air, helps you plan your work—especially if you need precise timing for intricate moulds or quick turnarounds. One-part silicones that dry with air are rare and generally not suitable for detailed mould making.