Undyed defects (white specks) that are visible on the surface of dyed cotton textiles have been associated with undeveloped fibers from motes (1, 2). Undeveloped fibers have a flat, ribbon-like structure because they are composed of only a very thin primary wall, or primary wall and beginning layers of secondary wall. These undeveloped fibers can form defects in several ways, depending on the thickness of their walls, and the type of processing they have undergone. Fibers with only primary wall remain compressed in bundles even when bolls open and the fibers dry. Fibers in these clumps can remain in their compacted state through processing, and appear on dyed fabrics as white specks. They do not accept dyes used for cotton fabrics because of their low cellulose content. Fibers whose secondary walls have begun to develop appear as separated fibers but still have a flat, ribbon-like appearance. These fibers tangle and form knots that may include bundles of unseparated fibers, mature fibers, or other plant parts.

Processing can also affect the structure of white speck defects. Some fiber bundles sit on the fiber surface as if they were simply deposited there. Others, however, are pressed flat into the fabric, covering one or more yarn areas. Additionally, if fibers have undergone extensive carding, the undeveloped mats or fiber knots can be separated or stretched to form more small mats, or longer and thinner knots. These fiber masses, separated by processing, can appear as white streaks. They may be less evident than white specks, but are still unacceptable defects.