A fiber manufacturer's customers demand consistency in performance from the fibers provided by the manufacturer. In other words, the manufacturer's customers require that the properties of any particular fiber not vary appreciably from batch to batch of that fiber as the different batches of that fiber are produced over several years. The fiber manufacturer, however, has a need to be able to identify fiber from different production batches, while maintaining the consistency and uniformity that the customers require. Much notoriety has been given to fiber identification in criminology, for example, as a way to bring murderers or other criminals to justice. Manufacturers also, however, have other more mundane and practical reasons for needing to identify the production batch of particular fibers. So it has long been desirable to find a cheap yet effective system for identifying fibers. Previously, for instance, one method has been to add a chemical or nuclear marker to the fiber, but this method has added expense and complications and has had disadvantages, such as the ease with which some one other than the fiber manufacturer can add the same marker, after manufacture, and so confuse this system for identification.
In particular, there has long existed a need for an economical way to identify and differentiate resilient hollow fibers (especially polyester hollow fibers) that are crimped and used as fiberfill in products such as baits, fiberballs and other filling materials and filled articles, such as pillows, filled apparel, comforters, cushions and such like bedding and furnishing material. Such crimped hollow fibers have a single continuous void throughout the fiber length and include those disclosed by Tolliver in U.S. Pat. No. 3,772,137, having a void content of about 13 percent to about 25 percent, and a crimp frequency of about 5 to about 12 crimps per inch (about 2 crimps per cm to about 5 crimps per cm), and a crimp index of about 25 to about 35. As indicated, it is important that any identifier system should not change the performance and properties of the fibers.