Slag foamingSlag foaming remains an active research area in high temperature processingHigh temperature processing due to its significant impact on processProcess efficiency. However, fundamental understanding of slag foamingSlag foaming is still limited. One important factor is the formation of solid particles, as a direct consequence of sub liquidus operations. These particles are known to strongly stabilize slag foams. However, the influence of precipitationPrecipitation-prone conditions on foam formation has not yet been thoroughly investigated. In this study, the effect of particle formation on slag foamingSlag foaming was examined through a series of experiments conducted at 1350 to 1500 °C using an Al2O3-CaO-Fe2O3-SiO2 slag system. The results show that the presence of particles significantly increases foam height. We therefore propose the Kaptay Factor, which is a pre-factor correcting the classic foam index models for the presence of particles in the foam layer, increasing the foam height up to 1.75 times greater than those predicted by conventional foam index-viscosityViscosity models.