Mercerised cotton is a type of cotton fabric or yarn that has undergone a textile finishing treatment called mercerisation. This treatment involves passing the cotton fabric or yarn under tension through a cold solution of 20-26% caustic soda, which causes the fibers to swell. The process was invented by John Mercer in 1844, who discovered that the treatment shrank the fabric and increased its tensile strength and affinity for dyes. The improved lustre of mercerised cotton is due to the production of nearly circular cotton fibres under tension. The benefits of mercerisation include improved dye uptake, tear strength, reduced fabric shrinkage, and a silk-like luster. Mercerised cotton is also stronger, smoother, and more resistant to mildew than non-mercerised cotton. The process also increases the absorption of dyestuffs by as much as 25%, making the color of the dyed cloth brighter and deeper. Mercerised cotton is commonly used in a variety of applications, including polo shirts, cotton sheets, and khakis. It is also used in crochet threads, where it imparts a silky, vibrant look that sets it apart from non-mercerised materials.