A technique where short lengths of unspun roving or yarn ends are knitted or woven into the fabric. The ends are left loose on the inside of the garment, creating a dense, fuzzy layer that eventually felts together with wear. This traditional method is used primarily in cold-weather accessories like mittens to provide extreme insulation.
Heard on the job
I'm making a pair of thrummed mittens to handle the subzero temperatures this winter.