AbstractTwo models, one physical and the other empirical, have been applied to the characterization of emission data of thin film products tested in small environmental chambers and have been compared in temts of emission results and m e of use. The physical model, being based on equations with coefficients bearing a physical meaning, is, in principle, more informative than the empirical one. However, it is uncertain whether it always gives accurate and unambiguous results. Moreover, in orakr to be exploited in a reasonable amount of time, it requires the use of non‐linear regression routines, e.g. those fom SAS Institute Inc., implemented on mainframes and, even then, it is often quite diffiult to handle. The empirical model does not rely explicitly on physical effects. Although by definition it can only describe but not interpret the experimental data, it does estimate parameters describing the emission with an accuracy comparable to that of the physical model. It is easier to handle than the latter as it can employ non‐linear regression routines such as those used on personal comput