Slub yarn

Slub yarn is a yarn into which thicker spots (slubs or flames) are intentionally built during spinning. Irregular mass distribution along the yarn length creates in the finished woven or knitted fabric a naturally uneven surface look reminiscent of handspun or vintage textiles. The effect can be precisely set: from fine barely visible slubs to pronounced thick knots every 10-30 cm.

Slub yarn is produced on ring-spinning machines with programmable drafting: the draft is briefly reduced so more fibres enter the yarn and a thickening occurs. Electronic controls (Uster Tester, Amsler Slubby) define slub length, frequency and random distribution. Alternatively slubs are produced mechanically via variable gears or needle-band webs.

Slub yarn is central to the vintage look in denim (slub denim) and linen-look cotton. Uniqlo, Levi's and Wrangler use slub effects for jeans with character; in T-shirts they add a slightly rustic feel. Downside: mechanical stress concentrates on the thicker spots and can lead to tears; premium slubs are made from strong cotton or cotton-linen blends.