Reviewing hygrothermal input data published in handbooks such as ASHRAE or ASTM, one often finds large range of variability in hygric properties of construction materials. Two factors that cause variability of these results are uncertainty of the test method and inadequate characterization of the material sample. Adequate characterization of the tested sample, despite being one of the most critical aspects of any material property measurement, is however frequently neglected. Yet, performing a high-precision test when the sample is not adequately characterized does not tell us what material was tested and therefore is not precise.
Typically porous materials are characterized with geometrical properties such as mean pore size and pore-size distribution, but this approach bring as many new questions as it addresses. In this context, a position paper from CIB W40 written almost 10 years ago proposed using critical hygrothermal characteristics for material characterization as well as for the input to the models. Yet, with a few recently completed PhD, revisiting this issue may support the use of hygrothermal models for field performance calculations.