05 Jan R-Values: The True Measure of Bulk Insulation Performance
You’ve probably seen the term R-Value mentioned whenever insulation or thermal resistance is discussed. It is a critical metric used to measure how effectively a material resists conductive heat flow. In simple terms, a higher R-Value indicates better thermal performance—contributing directly to improved indoor comfort and energy efficiency.
This standard is used worldwide to compare the effectiveness of bulk insulation materials.
The calculation of R-Value is straightforward and depends on two key factors:
- The thickness of the insulation, where increased thickness improves resistance to heat flow
- Thermal conductivity (k-value or lambda), which measures how easily heat passes through a material—the lower the k-value, the better the insulation performance
These factors are expressed in the following formula:
R-Value = Thickness ÷ Thermal Conductivity (k-value)
This relationship explains why insulation performs best when sufficient thickness is combined with low thermal conductivity. In glass mineral wool, thermal resistance is achieved through a network of fine fibres that trap air. Because air is a poor conductor of heat, these trapped air pockets play a crucial role in insulating performance.
While density does influence fibre arrangement, increasing density does not automatically improve R-Value. Beyond approximately 24 kg/m³, further increases in density offer limited additional benefit, as the added compaction slightly reduces the volume of trapped air, which is essential for thermal resistance. Understanding these relationships allows designers and specifiers to have an informed choice about the specification of the insulation products.