Rock Wool Thermal Efficiency Loss Due to Moisture Content
This chart is from a study about conventional insulation materials and loss of thermal efficiency due to moisture content.
The study, Temperature and Moisture Dependence of the Thermal Conductivity of Insulation Materials, covered conductive insulation materials ranging from rock wool to foam glass to perlite, at temperatures from 32 F/0 C to 176F/80 C.
The study’s summary is as follows: “Insulation materials are exposed to environmental influences (i.e. rain or humidity). Due to diffusion processes as a consequence of gradients of the temperature or the humidity, the moisture content of the insulation can increase. High temperatures at high moisture contents lead to a strong increase of the effective thermal conductivity because of pore diffusion.” In other words, conventional insulation materials conduct more heat when wet. In the chart below, derived from figures in the study’s “Figure #4, conductive loss causes rock wool to yield a thermal conductivity at or close to the same k values as wood fiber board, plaster wood lathe, water or window glass temperatures. We added the other materials’ k values to provide a comparison to rock wool’s wet insulation k value.