R-value is a measure of thermal resistance, measuring the heat transfer through a material per unit of area. This measure is used widely in the construction trades, both residential and commercial.
The r-value of rockwool insulation and mineral wool insulation varies widely. It really depends on what form the wool is in.
Press or formed rolls and sheets will have a different thermal resistance than loose fill type insulation. Blown rockwool insulation r value is approximately R-3.1 to R-4.0.
Rockwool R Values in Practice
In general, you can increase the r-value of a given wall by increasing the thickness or density of the insulator. For a simple example, if you were to triple the thickness of fiberglass batting in a wall cavity, the r-value would also triple.
However, if you were to forcibly press two layers of insulation into the thickness of one, you will get more r-value but most likely not a double r-value because it is improperly installed.
The r-value published by manufacturers applies strictly to insulation that is installed in a proper fashion.
Finishing off a wall with paneling or sheet rock does not provide a substantial additional r-value.
R values are usually given without their units, so it can be confusing what a value of “R-4.0” refers to. In most places in the world, the r value is given in international system of units (SI), while in the United States it is more common to use traditional US units.
The trick to remember is US r-values are around 6 times larger in magnitude than SI r-values. If you have an understanding of that you can quickly decipher what units you are dealing with.
SI units: m²·K/W US units: ft²·°F·h/Btu.
Typical R-Values for Insulations
Here is a useful table of r values from Colorado Energy.