Abstract: A mop for dusting use having and an excellent washing resistance employing a special thick cotton folded yarn as mop-head piles, the folded yarn but having a loose twist just within a specific range of twist number calculated from the formulas exhibited in the instant specification and are mercerized under the specific conditions to be contracted over 10 to 30% of the original yarn length. The dimensional and configurational stabilization and fixation of the twisted form of folded yarn are the intended aim of the mercerizing treatment, which realize the retainment of the twisted form, pliability and free mobility of individual pile in mop-head, even though the mop is subjected to severe washing treatment repeatedly.