1. Fibers & textile Analysis
CHAPTER 4
Fibers & textile Analysis
Forensic Science: Fundamentals & Investigations, Chapter 4

2. Introduction
Fibers are used in forensic science to create a link between crime and suspect
Through normal activities
We shed fibers
We picked up fibers
Very small fibers are classified as trace evidence
Collecting fibers within 24 hours is critical
Forensic Science: Fundamentals & Investigations, Chapter 4

3. How Forensic Scientists Use Fibers
Fiber evaluation can show
Type of fiber
Color
Possibility of violence
Location of suspects
Point of origin
Forensic Science: Fundamentals & Investigations, Chapter 4

4. Fiber Evidence
Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. 
They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. 
For analysis, they are first determined to be natural, manufactured, or a mix of both.

5. Sampling and Testing Shedding—common form of fiber transfer
Microscopes reveal characteristic shapes and markings
Infrared spectroscopy reveals chemical structures to differentiate similar fibers
Destructive Testing Methods
Burning fibers
Dissolving fibers in various liquids
Forensic Science: Fundamentals & Investigations, Chapter 4

6. Testing for Identification
Microscopic observation
Burning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue
Thermal decomposition—gently heating to break down the fiber to the basic monomers
Chemical tests—solubility and decomposition

7. Forensic Fiber Analysis
Why would this information be valuable to a forensic scientist?
Forensic Fiber Analysis
The world produced approximately 80 billion pounds of fabric in 1995, about half of which was cotton
The other approximately 44 billion pounds of fiber were manufactured or synthetic.
Table 1. U.S. Annual Production for Manufactured Fibers: 1995 (millions of pounds)
Fiber
Product
Polyester
3,887
Nylon
270
Olefin
521
Rayon/Acetate/Triacetate
498
Acrylic/Modacrylic
432
(Table 1 [6]). All these fibers were used in a variety of applications including but not limited to clothing, household textiles, carpeting, and industrial textiles.
It could be argued that the large volume of fibers produced reduces the significance of a fiber association discovered in a criminal case. It can never be stated with certainty that a fiber originated from a particular textile because other textiles are produced using the same fiber types and color. The inability to positively associate a fiber to a particular textile to the exclusion of all others, however, does not mean that a fiber association is without value. Considering the volume of textiles produced worldwide each year, the number of textiles produced with any one fiber type and color is extremely small. The likelihood of two or more manufacturers exactly duplicating all of the aspects of the textile is extremely remote (see endnote 2). Beyond the comments made previously about color, shade tolerance differs between dyeing companies. Therefore, color may vary demonstrably from batch to batch. Also, the life span of a particular fabric must be considered. Only so much of a given fabric of a particular color and fiber type is produced, and it will eventually end up being destroyed or dumped in a landfill.

8. Forensic Fiber Analysis
It could be argued that the large volume of fibers produced reduces the significance of a fiber association discovered in a criminal case.
Considering the volume of textiles produced worldwide each year, the number of textiles produced with any one fiber type and color is extremely small.
The likelihood of two or more manufacturers exactly duplicating all of the aspects of the textile is extremely remote

9. Sampling and Testing
Compare fibers found on different suspects with those found at the crime scene
Forensic Science: Fundamentals & Investigations, Chapter 4

10. Fabric Natural—animal, vegetable or inorganic
Fabric is made of fibers. Fibers are made of twisted filaments
Types of fibers and fabric
Natural—animal, vegetable or inorganic
Artificial—synthesized or created from altered natural sources

11. Fiber Classification —Natural Fibers
Animal fibers (made of proteins):
Wool and cashmere from sheep
Mohair from goats
Angora from rabbits
Hair from alpacas, llamas, and camels
Silk from caterpillar cocoons (longer fiber does not shed easily)
woven wool textile
Forensic Science: Fundamentals & Investigations, Chapter 4

12. Fiber Classification —Natural Fibers
Plant fibers (made of the polymer cellulose):
Absorb water
Insoluble in water
Very resistant to damage from harsh chemicals
Dissolvable only by strong acids
Becomes brittle over time
Forensic Science: Fundamentals & Investigations, Chapter 4

13. Fiber Classification —Natural Fibers
Plant fibers:
Cotton—most common textile plant fiber (picture)
Coir from coconuts is durable
Hemp, jute, and flax from stems grow in bundles
Manila and sisal from leaves deteriorate more quickly
Forensic Science: Fundamentals & Investigations, Chapter 4

14. Fiber Classification —Natural Fibers
Mineral Fibers:
Fiberglass—a fibrous form of glass
Asbestos—a crystalline structure
Forensic Science: Fundamentals & Investigations, Chapter 4

15. Fiber Classification —Synthetic Fibers
50% of fabrics are artificially produced
Examples:
Rayon
Acetate
Nylon
Acrylic
Polyester
Forensic Science: Fundamentals & Investigations, Chapter 4

16. Fiber Classification —Synthetic Cellulose Fibers
Regenerated Fibers (derived from cellulose):
Rayon
Most common in this group
Imitates natural fibers, but stronger
Celenese®
Cellulose chemically combined with acetate
Found in many carpets
Polyamide nylon
Cellulose combined with three acetate units
Breathable and lightweight
Used in performance clothing
Forensic Science: Fundamentals & Investigations, Chapter 4

17. Fiber Classification —Synthetic Polymer Fibers
Polyester
“Polar fleece”
Wrinkle-resistant
Not easily broken down by light or concentrated acid
Added to natural fibers for strength
Nylon
Easily broken down by light and concentrated acid
Otherwise similar to polyester
spandex nylon
Forensic Science: Fundamentals & Investigations, Chapter 4

18. Fiber Classification —Synthetic Polymer Fibers
Acrylic
Inexpensive
Tends to “ball” easily
Substitute for artificial wool or fur
Olefins
High performance
Quick drying
Resistant to wear
Forensic Science: Fundamentals & Investigations, Chapter 4

19. Comparison of Natural and Synthetic Fibers
Visual Diagnostics of Some Common Textile Fibers
under Magnification
Forensic Science: Fundamentals & Investigations, Chapter 4

20. Yarns, fabrics, and textiles
Yarns—fibers (of any length, thick or thin, loose or tight) twisted or spun together
Blending fibers meets different needs (e.g., resistance to wrinkling)
Fibers are woven into fabrics
or textiles
Threads are arranged side by side (the warp) More threads are woven back and
forth crosswise through the warp
Forensic Science: Fundamentals & Investigations, Chapter 4

21. Weave Patterns
Forensic Science: Fundamentals & Investigations, Chapter 4

22. Fiber Forensics
Generally, the analyst gets only a limited number of fibers to work with—sometimes only one.
Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home
Fibers are laid side by side for visual inspection through a microscope.

23. Fiber Evidence
Fiber evidence in court cases can be used to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers weighed heavily on the outcome of the case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims.