If insulation sized for 6 ¼ inches is stuffed into a 5 ½-inch wall cavity, the effectiveness of the insulation will?

When insulation that is sized for a larger thickness, such as 6 ¼ inches, is compressed into a narrower wall cavity of 5 ½ inches, its effectiveness decreases. Insulation materials rely on air pockets to resist heat flow, thus maintaining a home’s thermal efficiency. When insulation is compressed, as occurs in this situation, the material's ability to trap air is diminished, leading to a reduction in its R-value, which measures thermal resistance. The reduced thickness also limits the insulation's effectiveness in preventing heat transfer, resulting in a less energy-efficient wall assembly. Therefore, utilizing insulation that doesn’t properly fit the cavity leads to a decrease in overall performance.