A comprehensive research project on the fire performance of a new light mineral wool has been carried out at ETH Zurich in collaboration with the Swiss Federal Laboratories for Materials Science and Technology (EMPA). A large number of small-scale fire tests permitted the analysis of different parameters on the fire performance of the new mineral wool. The results of the fire tests allowed the verification and calibration of thermal properties used for thermal finite element (FE) analysis. Based on an extensive FE parametric study, the coefficients for the new mineral wool to be used in the design model for the verification of the separating function of light timber frame wall and floor assemblies were calculated. The paper first describes the main results of the experimental and numerical analyses. Then, the calculation of the coefficients for the new mineral wool to be used in the design model are presented.