For over 50 years, traditional insulation like fiberglass has been measured by one attribute, R-value. Due to the way R-value is tested, it only measures heat transfer by touch, or conduction. On the other hand, spray foam has an impact on all three forms of heat transfer, conduction, convection and radiation.
Conduction – performance is based on physical R-value
Convection – spray foam provides an air barrier, reducing heat transfer by air movement
Radiation – when installed under a radiant surface, such as a hot roof, the interior surface temperature is significantly lowered, thus lowering the radiant heat load