A fluid mechanical model was elaborated for the formation of mineral wool in the Junkers production technology. The model is based on an analytical approach. The future aim of the model is to establish guidelines for the following improvement in mineral wool quality: reduction of the diameter of mineral wool fibers, improvement of the homogeneity of fiber diameter distribution, and reduction of gravel size. The mineral wool is considered herein as reinforcing material for polymer composites, and such modifications result in the quality improvement of the composites. The quality improvement can be carried out by modifications of the technological settings. The parameters of the model were approximated on the basis of electron-microscopic measurements on a mineral wool reference specimen.