Slub yarn refers to yarn that has been purposely spun with slubs (thicker sections along the yarn). While it was once seen only as a defect, slub yarn is now intentionally created to give fabric more personality.

By spinning slub yarn with predictable, repeating slubs, the material woven from it develops roves, or intentional patterns within the fabric. However, slub yarn reduces the durability of the fabric as the yarn then inherently has weak spots.