A. Corresponding editor Paul Fisette responds: I believe that the energy benefit of this sheathing product is marginal at best — for all practical purposes, the benefit is nonexistent in cold to moderate climates. The R-value of the sheathing is less than the R-value of 1/2-inch OSB or plywood. The manufacturer’s energy claims are based on the ability of the foil to reflect radiant heat. In order for foil to work as a reflective barrier, an air space must be maintained on at least one side. If the reflective surface comes in contact with another surface on both sides — for example, siding on one side and insulation on the other — then heat can be conducted through the sheathing, and the amount of reflected radiation will be insignificant.
The other problem is that the foil surface’s ability to reflect radiant energy works best when it is bright and shiny. When the surface collects dust, the reflective efficiency drops.
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