In the 1970s Polyurethane spray foam came into the market. Some people had problems with formaldehyde allergies due to improperly cured applications. I believe there is also a kind of foam (not sure if it's a spray foam?) that produces cyanide gas if a home catches fire. What is the current status of spray foam insulation: are the products still formaldehyde-based or cyanide-generating, or have new, safer spray foam chemical solutions come to market? I recently toured a model home by Beazer in The Woodlands, TX that uses Certainteed's spray foam and sealant product applied directly to the underside of the roof, inside the attic (between joists) - even in a 90 degree Houston summer afternoon, the attic was 80 degrees and they even had a chocolate bunny sitting in the attic, unmelted, showing the amazing insulating efficiency of spray foam. Is this safe technology: Does it require other code requirements such as extra thick drywall, etc. to be considered fire barrier safe, etc? Just curious what TOH readers know; the technology seems very impressive.