Which of the following typically results in reduced R-value of insulation?

The correct choice reflects that compression in tight spaces reduces the R-value of insulation. R-value is a measure of thermal resistance, and it indicates how effective insulation is at resisting heat flow. When insulation is compressed—especially in tight spaces where it may be squished or tightly packed—it loses some of its ability to trap air. This air is critical for providing insulation because it acts as a barrier to heat transfer. Therefore, when insulation is compressed, its ability to resist heat flow diminishes, leading to a lower R-value.

Moisture penetration does impact insulation's performance but primarily by allowing heat transfer to occur more readily, rather than directly affecting the R-value in the same manner as compression. Age-related decay typically concerns the physical degradation of insulation materials, which can also affect their R-value. However, incorrect installation can lead to other issues like gaps or improper placement but does not specifically relate to the direct R-value loss attributed to the physical compression of the material itself. Thus, compression is the most accurate answer in the context of reduced R-value.