ABSTRACT Removal of foreign matter from cotton during the ginning process is a complex interaction of genetic traits, moisture differentials and machine performance parameters. Studies over a three-year period of over 30 cotton cultivars grown in Mississippi and South Carolina and processed identically at the gin, indicated that large differences occur in the initial foreign matter and in the foreign matter removal characteristics (cleanability) of cotton cultivars. Cleaning efficiencies also differ for the types of gin cleaning machinery such as seed cotton cleaners and lint cleaners. Overall cleaning efficiencies adjusted each year to a common level of foreign matter for each cultivar ranged from a low of 75.2% to 85.6%. Differences in cleaning levels occurred between years but the relative efficiencies remained similar for the cultivars.