The number of different fibers used in the textile industry is quite large. Identification of these fibers is frequently difficult since it is usually not possible to distinguish one fiber from another merely by touch or sight. Other tests must be performed. There are advantages and disadvantages to each. Some are easy, quick and relatively inexpensive，but do not allow clear distinctions to be made between fibers with the same characteristics. For example, a burning test will not differentiate between flax and cotton since both have the same burning properties. Others enable positive identification, but require much more time and more sophisticated testing apparatus (e. g. chemical analysis).
1. Burning test
The burning test is a good preliminary test. It provides valuable data regarding appropriate care and will help place a fiber into a specific category. It is not, however, a test that can be used alone to provide exact identification of specific fibers. In the case of yarns composed of two or more fibers, the test will usually give the reaction of the fiber that burns most easily; if a fiber is heat-sensitive，it will tend to melt or withdraw from the flame, leaving the flammable fiber to burn.
Burning Characteristics of Textile Fibers
|Fiber||Burn or melt||Shrinks from flame||Odor||Residue||Other properties|
|Cotton||Burns only||No||Burning paper, leaves or wood||Fine, feathery, gray ash||/|
|Flax, hemp, jute, ramie, etc.||All burning characteristics same as cotton|
|Rayon||All burning characteristics same as cotton|
|Wool, mohair, cashmere, alpaca，etc.||Burns only||Yes||Very strong odor of burning hair||Black, hollow irregular bead which crushes easily to a gritty, black power||Self – extinguishing|
|Silk||Same as wool, except odor is not so strong and may smell like charred or burning meat ( no sulphur content like wool)|
|Acetate||Burn & melt||Yes||Combination of burning paper and vinegar||Dark, hard, solid bead||/|
|Acrylic||Burn & melt||Yes||Broiled fish||Hard, irregularly shaped bead||Flame gives off black smoke|
|Aramid||Burn & melt||Yes||Sweet||Hard, black bead||Self – extinguishing|
|Glass||Melt only||Very slowly||No odor||Hard, whitish bead||Flame resistant fiber； heat from match will not cause fiber to melt|
|Modacrylic||Burns and melt||Yes||Chemical||Hard, black irregular bead||Self – extinguishing|
|Nylon||Burns and melt||Yes||Celery||Hard, cream – colored bead. If fibers are overheat， bead will become dark||drops of melted fiber may fall from heated portion of sample|
|Olefin||Burns and melt||Yes||Chemical||Hard, tan bead||Flame gives off black smoke|
|Polyester||Burns and melt||Yes||Sweet chemical||Hard，cream — colored bead. If fibers are overheat, bead will become dark||Drops of melted fiber may fall from heated portion of sample; flame gives off black smoke|
|Spandex||Burns and melt||Yes||Chemical||Soft, black ash||/|
|Vinal||Burns and||Yes||Paraffin – like or Chemical||Hard, tan bead||/|
Remember that the burning test is a preliminary test indicates general grouping or categories only. The test is relatively simple but must be used with care to avoid injury and guard against fire.
2. Microscopic evaluation
Most fibers provide different view of both their lengthwise and crosswise. Natural fibers have their specific shape in their cross- section，and man-made fibers are similar in their microscopic appearance.
3. Chlorine bleach test
For silk or wool fibers，they will be wet with liquid chlorine bleach，these fibers turn yellow and after a while disintegrate from the action of the chemical.
4. Dry and wet strength test
The strength of many fibers is affected by the amount of water they contain, a few fibers get a little stronger when wet, such as cotton fibers; some retain about the same in strength; and others get weaker.
5. Stain test
The stains are a mixture of several different classes and colors of dyes so that each fiber will be dyed a specific color.