Based on comparison of properties of the inorganic composition of various cotton dusts, this paper demonstrates that cotton dusts <20µm in diameter separated from card room condenser trash material are very similar chemically to dusts collected in that same environment by a vertical elutriator cotton dust sample. A method to estimate the fraction of cotton dust from sources such as cotton leaf and bract, humidifier water solids, soils and background ambient air is given. Data from dusts obtained from the North Carolina State Model Card loom and data on dusts reported in the literature are compared. In a study of 24 bales of cotton processed in the Model Card Room, it was estimated that 26%, of the elutriator dust was from humidifier water solids, less than 15% from ambient air and soils, and the remainder mostly from cotton bract and leaf.