How long it takes for spray foam to harden depends on type of foam, temperature, humidity, and thickness, but generally spray foam becomes tack free and expands within seconds to minutes after application and hardens enough to handle within minutes to hours. One component canned expanding foam like Great Stuff becomes tack free in 10 to 20 minutes, can be cut or trimmed in 1 to 2 hours, and fully cures in 8 to 24 hours depending on bead size and humidity, as it cures with moisture in air. Two component professional spray foam insulation, both open cell and closed cell, expands and becomes tack free within 10 to 30 seconds after spraying, can be walked on or handled in few minutes, and fully cures within 24 hours, though it reaches most of its strength within minutes. Full cure and off gassing may take 24 hours, so occupants are often advised to stay out for 24 hours after installation. Cold temperatures slow curing, warm and humid conditions speed curing. So spray foam hardens quickly within minutes but fully cures in up to 24 hours.
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