Experimental and theoretical studies are reported on formation of primary particles during evaporation of metals into a host gas in an evaporation chamber. The developed theory explains present and previous experimental observations of this process. The dependence of primary particle size on host gas pressure, host‐gas molecular weight and source temperature has been explained. Particle thermophoresis has been shown to cause formation of the so‐called ‘‘smoke shell’’ observed surrounding the vapor source. Coalescence of primary particles has been shown not to be an important growth process for the primary particles, although for longer times primary particle coagulation produces the chains of primary particles observed experimentally.