in textiles, a chemical treatment applied to cotton fibres or fabrics to permanently impart a greater affinity for dyes and various chemical finishes. Mercerizing also gives cotton cloth increased tensile strength, greater absorptive properties, and, usually, a high degree of lustre, depending on the method used.

The treatment consists of immersing the yarn or fibre in a solution of sodium hydroxide (caustic soda) for short periods of time, usually less than four minutes. The material is then treated with water or acid to neutralize the sodium hydroxide. If the material is held under tension during this stage, it is kept from shrinking appreciably; if no tension is applied, the material may shrink by as much as one-fourth. Higher-quality cotton goods are usually mercerized; cloths so treated take brighter, longer-lasting colours from less dye. The effect of caustic soda on cotton was discovered in 1844 by John Mercer, an English calico printer, who received a patent for it in 1850.