Isothermal cold chamber tests indicate that the NEI TB-1 pyrotechnic used in FACE after July 1975 emits a silver iodide smoke which has a much greater nucleating effectiveness in the temperature range −6 to −12°C than that emitted from the Olin pyrotechnic in predominant use in FACE prior to August 1975. The NEI TB-1 pyrotechnic was also found at “warm” temperatures to have a higher nucleating effectiveness than the U. S. Navy WMU-9 flare which also contains the TB-1 formulation. From transmission electron microscopic analyses, the size distributions of the particles produced from all three types of flares were found to be similar. Because of the small sizes of the particles (mean diameter ∼0.03 μm) a diffusive contact mechanism probably is playing an important role in the nucleation of water droplets. It is postulated that soluble potassium iodide, present in a complexed form, is detrimental at warm temperatures to the nucleating effectiveness of particles produced from the Olin pyrotechnic. Differences in nucleating effectiveness in the two TB-1 mixtures are attributed to the presence of small amounts of chlorine in the binding material of the NEI pyrotechnic.