What is the difference between open and closed cell foam?

There are three major differences. First, SPRAYTITE® technology uses the versatility of polyurethane chemistry to offer a closed-cell content of greater than 90 percent, and open-cell foams commonly used as insulation systems have approximately 60 percent open-cell content. Second, closed-cell content offers an R-value of over 6.6-6.9 per inch and open-cell offers between 3.7 and 4.1 per inch. Third, closed-cell foam is virtually impermeable to air and moisture, while open cell foam allows far more air and vapor into the building interior. In addition, closed-cell foam is very resistant to bulk water absorption and for that reason, closed-cell spray foam (and rigid board foams) are the only products considered flood-damage resistant by the Federal Emergency Management Agency (FEMA).