What is mercerized cotton?
Mercerized cotton is cotton yarn treated with caustic soda under tension, which adds luster, strength, and deeper color. Ideal for dress socks.
What mercerization does
Mercerization is a finishing process for cotton yarn. The yarn is treated with a caustic soda solution while held under tension, which makes the cotton fibers swell and become rounder and smoother.
That change brings three benefits buyers can see and feel:
- Luster: smooth, round fibers reflect light, giving a subtle sheen.
- Strength: the yarn resists abrasion better than untreated cotton.
- Color: dyes absorb more deeply, so colors look richer and fade less.
Where it is used
Mercerized cotton, sometimes sold as fil d’Ecosse, is the classic yarn for dress socks knitted at a fine gauge. It is usually made from long-staple combed cotton, which already starts smoother and stronger.
Things to know
It costs more than standard cotton and feels cooler and less fluffy. Like any cotton sock, a mercerized sock still needs some synthetic content for durability and stretch; a typical recipe blends the cotton with polyamide and elastane.