Aiming to improve the comprehension of the expansion process of perlite, a numerical study has been carried out, concerning the water vapour bubble growth in softened perlite melt. The physical properties of the melt and temperature history during the expansion process are varied, in order to determine the most influencing parameters. Calculated bubble growth results are compared to experimental data obtained in a previous study, and to industrial expansion results. An extensive literature review has been done to determine the physical properties of raw and expanded perlite, as input values to the numerical model.