The Collaborative International Dictionary of English v.0.48:

Slub \Slub\, v. t. [imp. & p. p. Slubbed; p. pr. & vb. n.
   Slubbing.]
   To draw out and twist slightly; -- said of slivers of wool.
   [1913 Webster]

WordNet (r) 3.0 (2006):

slubbed
    adj 1: of textiles; having a rough surface; "a sweater knitted
           of nubbly homespun yarns" [syn: homespun(p), nubby,
           nubbly, slubbed, tweedy]