Lapolla’s Foam-Lok FLX 500-EM Spray Foam just simplified the process of insulating attics and crawlspaces. That’s because it has been certified by the International Code Council Evaluation Service for use in uninhabited spaces without an ignition barrier—in other words, it can be left uncovered without drywall. The testing criteria require that the foam withstand an open flame for a specific time without igniting. The closed-cell version has an installed cost of $1 to $1.25 per square foot for every inch of depth, while the open cell runs $0.50 to $0.75.