How much does the foam expand, and how do I control density?

Expanding foams (FlexFoam-iT and similar) grow well beyond their liquid volume, the multiplier depends on the specific product and is on its TDS. Key points:

• Free-rise vs. constrained: in an open pour the foam rises to its natural density. In a closed/over-packed mold it's denser and harder, "packing" more material into a fixed volume raises density on purpose.
• Density is set by the product, not by mixing more. To get firmer foam, choose a higher-density grade rather than altering the ratio.
• Exotherm & 3D-printed molds: foams generate some heat as they rise. Be sure your mold material can handle high temperatures.
• Moisture sensitive: keep foam components sealed and dry, humidity ruins the rise and causes irregular cells.

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Related guide: Foam Problems