Safety Components - Ask the Experts

Changes Occur During Fibrillation and Oxidation. Expect it. Understand it.
Ballistic vests. Bridge reinforcements. Lightweight composites. Turnout gear outer shells and thermal liners. High performance
materials that share one common thread: DuPont™ Kevlar®. Developed by DuPont in 1965, DuPont™ Kevlar® is a para-aramid
fiber known to be one of the strongest fibers in the world. Offering strength noted at 5 times stronger than steel, para-aramid
fibers are the backbone in applications ranging from ballistic vests to large structures like buildings and bridges. In addition to
strength, para-aramid fibers also maintain integrity when facing high thermal exposures (temperatures in excess of 1000° F).
High strength and high thermal resistance make para-aramids the fiber of choice when making high performance outer shells
and thermal liners for structural turnout gear. Over 80% of the flame resistant outer shell fabrics in North America are blended
with para-aramid fibers. While Dupont™ Kevlar® (USA) is the most well known, additional para-aramid fiber brands include Teijin
Twaron® (Netherlands) and Teijin Technora® (Japan).

Engineered to Last
Where do the strength and toughness of para-aramid fibers come from?
The answer lies in the orientation of the polymer chains. High strength fibers possess high levels of crystallization, which
reduces elongation and increases fiber strength. Like DuPont™ Kevlar®, most high strength fibers experience a splintering of
the surface, or “fibrillation” of individual fibers after being crimped, washed, or strained. Fibrillation, a self-screening process
typical of high strength fibers, protects the core of the fiber while allowing gradual strength loss over time. With normal field
use and laundering all para-aramid reinforced outer shells undergo some level of fibrillation; less apparent in light colored fabrics,
more apparent in dark or black fabrics.

Download PDF Engineered for Performance
How does fibrillation affect the performance of outer shell fabrics?
Outer shell fabric performance is divided into 4 key areas:
• Thermal Stability
• Durability
• Comfort
• Appearance

Thermal Stability
Fibrillation does not negatively impact protection or flame
resistance. In fact, TPP usually increases after wash (when
fibrillation/lofting occur), because the fabrics become thicker
and more insulating (Chart A).

Durability
The use of high strength para-aramid fibers increases the tear,
cut, abrasion, and flame resistance of fabrics in the fire service.
Fibrillation will occur as the fabric is subjected to normal wear,
flexing, and repeated washing. However, fibrillation alone is not
a sign that a fabric has lost significant strength properties.
When cared for in accordance to NFPA 1851, outer shell fabrics
experience only minor and gradual strength loss over time (Chart B).

Comfort
Fiber fibrillation does not negatively impact comfort. After repeated use or washing, the fabric will become softer and more flexible.

Appearance
Once they are put into service, all para-aramid rich fabrics undergo some level of appearance change, typically caused by
fibrillation or oxidation.


Change In Appearance:
From Fibrillation
Para-aramid fibers start out with a smooth consistent appearance
(Figure 1). The process of fibrillation causes small/hairy fibrils to
form on top of the fiber core (Figure 2). The result is a fiber with
greater surface area, reflecting light differently than the original fiber.
This “frosting” of the surface is similar to what happens with a brown

glass bottle: if you grind down the glass bottle small enough the
remaining powder will appear white because the surface particles
dominate the reflected color. The substance of the glass remains
brown but it appears white, just as black para-aramid fibers
remain black yet they appear charcoal.

From Oxidation
After para-aramid rich fabrics are exposed to light the fiber’s surface
begins a process called oxidation. As a para-aramid oxidizes it
changes color: fabrics appear to get darker. This change in color
is similar to the way a copper penny appears green after oxidation.
Like a copper penny, the change in color from oxidation is normal
and not indicative of degradation. The rate at which a para-aramid
rich fabric darkens through oxidation depends on many factors.
These include the fabric blend, fabric design, and most importantly
the way in which the fabric or garment is stored (protected from light).
Sometimes turnout gear will fully oxidize in a day, other times it takes

weeks, and other times different panels of the garment will oxidize
(darken) at different rates. One thing is certain: the entire garment
will eventually oxidize and darken over time.

A closer look at an outer shell under a microscope
shows non-fibrillated DuPont™ Kevlar® fiber (Figure 1)
and fibrillated DuPont™ Kevlar® fiber (Figure 2).
After fibrillation the fiber reflects light in a different
cast. Darker fabrics like black shift from a rich dark
color to charcoal; lighter fabrics such as gold
may develop Figure 1: New fabric, unwashed DuPont™
Kevlar® fiber a hairy appearance.

Conclusion
Fibrillation and oxidation are common to all outer shells and thermal liners rich with para-aramid fiber.
It is important to understand the affects of fibrillation and oxidation to gain realistic expectations on
fabric appearance, durability, and performance.