The R-value is a measure of thermal resistance, indicating how well a material resists the conductive flow of heat. A higher R-value means better insulating effectiveness.
There are two ways to measure R-value: nominal and effective. Here's how the two concepts differ and why they both matter.
Nominal R-Value
The nominal R-value represents the stated insulation value of a specific material under steady-state, laboratory conditions. This is the R-value that is generally printed on the insulation packaging and is used in marketing and sales of insulation products.
An architect would use the nominal R-values in initial design phases to compare different insulating materials and to calculate an initial estimate of the overall thermal resistance of various building components.
The limitation is that nominal R-values are determined under ideal, standardized conditions, which means they may not fully represent the material's performance under the varying conditions in the real world (like changes in temperature, humidity, etc.).
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