A.Martin Holladay, editor of Energy Design Update, responds: The R-value of 3/8-inch-thick foil-faced bubble wrap is about 1.3. The R-value of 3/8-inch-thick foil-faced expanded polystyrene foam is about 1.6.

By contrast, 2 inches of extruded polystyrene insulation has an R-value of 10.

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