What is the R-value for 4 inches of polyiso insulation (R-5.7 per inch)?

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Multiple Choice

What is the R-value for 4 inches of polyiso insulation (R-5.7 per inch)?

Explanation:
R-value measures how much a material resists heat flow. For a single insulation layer, the total R-value is the thickness times the R-value per inch. With polyiso rated at 5.7 per inch, four inches yields 4 × 5.7 = 22.8. So the R-value is 22.8. This same idea applies when stacking layers—you add their R-values to get the total. For reference, numbers like 16.0, 20.0, or 25.6 would correspond to different thicknesses (roughly 2.8 inches, 3.5 inches, and 4.5 inches, respectively), not four inches.

R-value measures how much a material resists heat flow. For a single insulation layer, the total R-value is the thickness times the R-value per inch. With polyiso rated at 5.7 per inch, four inches yields 4 × 5.7 = 22.8. So the R-value is 22.8.

This same idea applies when stacking layers—you add their R-values to get the total. For reference, numbers like 16.0, 20.0, or 25.6 would correspond to different thicknesses (roughly 2.8 inches, 3.5 inches, and 4.5 inches, respectively), not four inches.

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