Non-fiber particles in cotton play an increasingly important role in cotton quality measurements. Trash and dust particles represent undesirable "foreign matter" in cotton fibers. This foreign matter originates at harvest from the cotton plant, from the surrounding soil, from adjacent grasses, and from other sources.

Foreign matter in cotton fibers affect yarn and fabric appearance, yarn evenness, yarn strength, reduces processing efficiencies, and are a part of many cotton grading systems.

Advances in mill processing have shown a trend to less contaminant tolerant systems driven by today's higher quality specifications on sliver, yarn, and fabric.

Economic decisions by cotton buyers have sent more low-grade cottons to mills in recent years. Low-grade cottons and recycled raw materials contain a comparatively high proportion of trash and dust, which can lead to larger deposits in rotors of open-end spinning systems.