An average grade of cotton that is usually used in denim.
Cotton is graded according to its strength, staple length, color, smoothness, and uniformity. Large amounts of leaf and debris decrease the cotton’s value. Middling grade cotton is considered average and is used as the standard to measure all other grades of cotton. It is a fleecy cotton with very small amounts of debris and is nearly white. Fair to middling cotton is an average grade of cotton, and is the type usually used for denim. Fair to middlin’ has also become an expression in the southern United States meaning okay to average in quality, as in “I’m feeling fair to middlin’”.
Here is fair to middling cotton: