R Values are not all created Equal
This is a topic that can mislead many and I wish to diffuse the confusion. I write this after a customer new to NZ was looking for much higher R Values from our 25mm HD XPS foams. Once we realised that my customer was accustomed to products in Canada & US, i shared the calculation below.
R Value ( insulation)
The R value or R-value is a measure of thermal resistance, used in the building and construction industry. The bigger the number, the better the building insulation's effectiveness. R-value is the reciprocal of U-value.
Around most of the world, R-values are given in SI units(metric), typically square-metre Kelvin per watt or m²·K/W . In the United States customary units, R-values are given in units of ft²·°F·h/Btu (imperial). It is particularly easy to confuse SI and US R-values, because R-values both in the US and elsewhere are often cited without their units, eg R-3.5.
To Convert Imperial (US) R Values to Metric (SI) R Values
R(imp)/5.678263 = R(SI)