R-value of about 19.5. The ICC-ES report for Home Foam Insulthane 100 (ESR-2360, issued September 1, 2007) lists a similar maximum thickness: âThe insulation, at a maximum thickness of 5 Â½ inches and. a minimum density of 0.43 pcf, has a flame-spread index of. not more than 75 and a smoke-developed index of not more.