Labelled or Nominal R-value – is the current industry standard for all building codes. Soon, (late 2013) Effective R-Value will become a recommended industry standard. Labelled R-value is the tested ability of insulation (by itself / no building materials) to resist the flow of heat energy. The temperature range is not conducive to real world environments. Typical testing temperature range: Warm side +21°C Cold side +10°C.
Effective / Performance R-value – is the tested ability of "Full Scale" real world wall assemblies including building materials and insulation to resist the flow of heat energy. The temperature range (-18°C to +21°C with a 22 KPH wind / -31°C Wind Chill) provides the real world (Effective) R-value of wall assemblies in predominately cold climates, i.e.: Canada. Results from this method of testing are highly reliable and are presently recognized and accepted by most building code jurisdictions. Click here to read what building science engineering says about R-value.