  The reliability of a model is its accuracy in predicting the physical
phenomena using the known input parameters. It also depends on the model's
ability to estimate relevant parameters using observations of the physical
phenomena. In this paper, the reliability of the VTT model is investigated
under these two criteria for various given temperature and relative humidity
constant in time. First of all, experiments are conducted on bamboo fiberboard.
Using these data, five parameters of the VTT model, defining the mold
vulnerability class of a material, are identified. The results highlight that
the determined parameters are not within the range of the classes defined in
the VTT model. In addition, the quality of the parameter estimation is not
satisfactory. Then the sensitivity of the numerical results of the VTT model is
analyzed by varying an input parameter. These investigations show that the VTT
mathematical formulation of the physical model of mold growth is not reliable.
An improved model is proposed with a new mathematical formulation. It is
inspired by the logistic equation whose parameters are estimated using the
experimental data obtained. The parameter estimation is very satisfactory. In
the last parts of the paper, the numerical predictions of the improved model
are compared to experimental data from the literature to prove its reliability.
