In the last century, the only cost-effective insulation for the home was mass insulation like fiberglass, cellulose and foam that reduced heat transfer by convection and conduction. The “R-value” was the measure of how good a job those insulators did. Yet R-value measures only the smallest part of residential heat transfer.
E-value is the measure of emissive, radiant heat transfer, the principle source of energy loss. New technologies make it practical to achieve extremely low emissive in window glass and in a reflective film ideal for the attic. As these low-E technologies advance, the codes will catch up and E-value will replace R-value as the primary measure of energy efficiency.

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R-value measures only the resistance to conduction and convection, but almost all of the energy lost in your home is through emission – radiant heat transfer. “E-value” (the ability to prevent radiant heat transfer) is far more important than R-value in evaluating an insulation system. eShield™ Attic Energy Barrier has a much higher E-value than any form of mass insulation.