Cloth Fibers

Like hair, cloth fibers are among the most common items left as trace evidence at a crime scene. Forensic scientists analyze, identify, and compare cloth fibers to place a suspect at a crime scene. For example, wool thread caught on a window frame at a crime scene may match the sweater found at a suspect’s house. Try the following activity to see how fibers can be used as evidence in an investigation.

Materials

- several different fabrics, including some with natural fibers, such as cotton and wool, and some with synthetic fibers, such as nylon or crayon
- transparent tape
- several sheets of white paper
- marking pen
- magnifying lens
- microscope (optional)
- pen and pencils
- notebook

NOTE: If you used old clothing, be sure to ask adult permission first, or ask at your local fabric store for fabric remnants.

Procedure

1. Pull fibers from several fabrics.
2. Tape each fiber to a separate sheet of white paper. With the marking pen, label the fiber according to which fabric it is from and how it was obtained.
3. Examine each fiber with the magnifying lens and microscope, if available. Record your observations in your notebook.

More Funs Stuff to Do

Ask a helper to pull a fiber from one of the fabrics without telling you which fabric it’s from. Using your labeled samples and magnifying lens or microscope, can you identify what the fiber is and which fabric it came from?

Explanation

There are four sources of fibers: animal, vegetable, mineral, and synthetic. The most common animal fibers are wool, cashmere, and silk. The most common vegetable fiber is cotton. Asbestos is the only mineral fiber. Synthetic fibers make up about 75 percent of all textile fibers in the United States and are the most common fiber investigated in the crime lab. There are over 1,000 different types of synthetic fiber, classified by their chemical composition, fiber shape and size, additives, and manufacturing process.

Like hair, fibers are important trace evidence. A forensic scientist use a vacuum cleaner to collect fibers, hairs, and dirt found at the scene of crime. These materials are then taken to the crime lab to be analyzed and compared to known samples. Investigators can link a suspect to the scene of a crime by matching fibers found at the scene of a crime to fibers found on a suspect or in a suspect’s vehicle or home.