1. Fibers

2. Forensic Examination of Fibers
Important evidence in incidents involving personal contact- homicide, assault, sexual
Cross-transfers may occur between the clothing of a suspect and victim
Hit-and-run victims can leave fibers, threads, or whole pieces of clothing on a vehicle
Fibers can also become fixed in screens or glass broken during a breaking-and-entering attempt

3. Natural Fibers Are derived from animal or plant sources
Animal fibers comprise most natural fibers encountered in crime lab exams
Can include hair coverings: sheep (wool), goats (cashmere), camels, llamas
Or fur fibers: obtained from mink, rabbit, beaver, etc.
Most common plant fiber is cotton

4. Manufactured Fibers Are derived from natural or synthetic polymers
They have increasingly replaced natural fibers in clothing & fabric
They are made by:
Processing raw material from cotton/wood pulp and extracting cellulose
The cellulose may be chemically treated and dissolved in a solvent
It is then forced through small holes of a spinning jet (spinneret) to produce the fiber
Fibers made from natural raw materials (regenerated cellulose) are called regenerated fibers: rayon, acetate, triacetate
Fibers made from synthetic chemicals are synthetic fibers: nylon, polyester, acrylic

5. Microscopic Exam of Fibers
The first and most important step is a comparison for color & diameter by a comparison microscope
Other features that may aid in the comparison are lengthwise striations (lined markings) on the surface of some fibers and pitting of the fiber’s surface with delustering particles (titanium dioxide particles added to reduce shine)
Cross-sectional shape of a fiber may also help

6. Analytical Techniques Used
Two fibers may seem to be the same color, differences may exist in the dyes applied to them when made
Most fibers are dyed with a mixture of colors to obtain a desired shade
Can use a visible light microspectrophotometer to compare the colors of fibers
A fiber as small as 1 mm long or less can be examined

8. Analytical Techniques Used
A more detailed analysis of the fiber’s dye composition can be obtained by a chromatographic separation of dye
Small strands of fibers are compared for dye content by extracting the dye off each fiber with a solvent and then spotting the dye solution onto a thin-layer chromatography plate
The dye of the questioned and standard fibers are separated on the plate and compared for similarity

9. Others
When fibers are compared, they must be shown to have the same chemical composition (belong to the same class)
For example, the standard and questioned fabric both being nylon instead of one being nylon while the other is cotton
Many manufactured fibers exhibit double refraction or birefringence which will make it look crystalline
Polarized white light will split into two rays that are perpendicular to each other and produce interference colors, polarization

10. Significance of Fiber Evidence
Once a match has been determined, the significance is bound to be raised
No technique can associate a fiber definitively to any single garment
No database is available for determining the probability of a fiber’s origin
Despite this, one should not discount the significance of a fiber match
By observing what people wear, it is unlikely to find two different people wearing identically colored fabric ( exception: jeans and cotton tees)
There are thousands of different colored fibers
Combine this with the fact that scientists not only compare color, but also size, shape, microscopic appearance, chemical composition and dye
There will still be a good chance of linking a questioned fiber to a standard

11. Collection and Preservation
Clothing should be packaged in paper bags
Each article must be placed in separate bags to prevent contamination
Must keep clothing from different people from coming into contact
Carpets, rugs, and bedding should be folded to protect areas suspected of containing fibers
Knife blades should be covered to protect adhering fiber
If a body was wrapped in a carpet or blanket, tape lifts must be done on the body
If individual fibers are found, they must be removed with clean forceps and placed in a small sheet of paper, must be folded and labeled and placed in another container

12. Types of Fiber Cotton (ribbon-like) Nylon Polyester
Rayon fibers Silk (fractures)
Wool