Can mold grow behind spray foam insulation?

Yes, mold can grow behind spray foam insulation if conditions allow moisture, improper installation, or existing moisture problem, though closed-cell spray foam itself is resistant to mold, it can trap moisture behind it if not installed correctly, similar to needing HEPA filtration to prevent mold from dust. Closed-cell spray foam is water resistant and does not provide food for mold, but if installed over wet wood, damp sheathing, or with water leaks, moisture can be trapped between foam and sheathing creating dark, damp environment where mold can grow on wood behind foam, not on foam itself. Open-cell spray foam is more vapor permeable and can absorb moisture, so if high humidity or leak, mold can grow on adjacent wood. Proper installation includes ensuring substrate is dry, no leaks, and adequate ventilation to prevent moisture trapping. If roof leak occurs, closed-cell foam can hide leak and allow mold growth behind before detected. So mold can grow behind spray foam insulation if moisture present and trapped, though foam itself resists mold, risk reduced by proper installation, drying substrate, fixing leaks, and maintaining ventilation, so inspection for moisture before installing is crucial to prevent mold behind spray foam.