Radon Diffusion Coefficients of Barrier Materials: A Critical Review of Measurement, Modeling, and Laboratory-to-Field Interpretation

Radon-resistant membranes and other barrier materials are widely used to limit soil-gas entry into buildings, yet published radon diffusion coefficients are difficult to compare because the reported measurand, boundary conditions, leakage treatment, and test conditions differ among studies. This critical review examines how these coefficients are measured, modeled, and compared, and why laboratory values do not necessarily predict installed barrier performance. The material diffusion coefficient, the effective coefficient of porous media, and the apparent coefficient obtained by fitting experimental data are distinguished, and the coefficient affected by each influencing factor is identified. Steady-state and transient methods are compared in terms of the quantity obtained, test duration, and dominant sources of bias. Illustrative calculations show that a fixture leakage conductance of only 10−11 m3 s−1 can inflate the apparent coefficient of a highly resistant membrane several-fold, that the Peclet number of an intact specimen can be far below unity while a sub-millimeter crack is advection-dominated, and that defects occupying less than 10−5 of the barrier area can dominate radon entry. Gas-side resistance, model-form uncertainty, mixed-mode transport, and thoron-specific constraints are also discussed. Harmonized reporting, joint and penetration testing, interlaboratory comparison, durability assessment, and laboratory-to-field validation are identified as priorities.