What are the negatives of spray foam?

Negatives of spray foam insulation include high upfront cost compared to fiberglass or cellulose, with professional installation costing two to three times more. Installation requires professional equipment and trained installers, and improper mixing or application can cause off gassing, lingering odors, and health issues if occupants return too soon. Spray foam can trap moisture if not correctly installed, leading to hidden rot in wood framing, especially closed cell foam that does not allow drying. It is difficult to remove or modify once cured, making future renovations or electrical work harder. Spray foam can make it harder to detect roof leaks because it covers rafters. Some spray foams use blowing agents with high global warming potential, though newer water blown foams are better. Open cell foam can be damaged by water and pests. Spray foam can also cause over insulation that reduces air exchange, requiring mechanical ventilation. Additionally, DIY kits have learning curve and can create mess and waste if not applied correctly.