Work out thermal resistance (r value) instantly with clear inputs, formula shown and shareable results.
R-value is thickness divided by conductivity, so it measures how strongly a layer resists heat flow per square metre. 100 mm of mineral wool at k = 0.038 gives R = 2.63 m2 K/W and a U-value of 0.38 W/(m2 K). Layers in series add their R-values, which is how a full construction is assessed.
R-value
R = thickness / conductivity
U-value
U = 1 / R(total)
Yes, for layers in series - including the internal and external air films, which contribute about 0.13 and 0.04 m2 K/W.
Because the imperial unit is about 5.68 times smaller. An R-13 batt in imperial is only R-2.3 in SI.