Expanded Polystyrene "EPS" White Board

EPS insulation is used in a wide range of applications including insulated concrete forms and structural insulated panels (SIPs). EPS has the lowest average R-value of the three most common types of rigid-foam insulation, around R-4 per inch.  However, as compared to ISO and XPS, EPS does not loose RValue over time due to thermal drift.  Most EPS is unfaced and is considered semipermeable to water vapor, so it does not create a vapor barrier.