Extruded polystyrene (XPS) insulation and polyisocyanurate (ISO) insulation are both closed-cell plastic foams, consisting essentially of the same chemical composition, and both have HCFC gas trapped in cell cavities. Yet their ?-values are different. The ?-value for ISO = 6.0 and that for XPS = 5.0. Why is that so?
What will be an ideal response?
ISO insulation board is has a facer laminated to it on its two faces (not on the four edges), while XPS is unfaced. The amount of HCFC gas leaking out of ISO is much smaller and hence, it has a higher ?-value.
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