TECHNICAL BULLETIN
UNDERSTANDING THE
DIFFERENCES BETWEEN
PBI vs PBO
PBI and PBO are acronyms for the fiber chemistry each represents. PBI is the trade name for polybenzimidazole, a fiber made by PBI Performance
Products, Inc. in Charlotte, NC. PBO, with the trade name of Zylon®, is a Polybenzobisoxazole fiber made by Toyobo in Osaka, Japan. PBI and PBO are
used in some of the same applications due to their ability to resist degradation from high heat and flame. One such application is the outer shell fabric
of firefighter turnout gear. Listed below are the most common outer shell performance characteristics and how PBI and PBO perform.
PROTECTION
Flame and thermal protection are the blocks from which any outer shell is built. An important factor in
the ability of a fiber to protect against high heat and flame is its stability when subjected to these
exposures.
Thermal Protection – Fibers that are highly conductive will increase the rate at which heat is
transferred into the composite and through to the wearer. The chart on the right illustrates the thermal
conductivity values for various fibers, including stainless steel as a point of reference. Note that Zylon®
transfers heat through the fiber more rapidly than stainless steel – a problem firefighters feel while
fighting a fire versus engaging in non-firefighting activities.
Flame Protection – The ability of a fiber to protect against flame impingement is its resistance to
melting, shrinking, and charring. The decomposition temperature is the temperature at which the fiber
begins to break down. Fibers with higher decomposition temperatures create fabrics with better break
open resistance to heat and flame. These higher decomposition temperatures help PBI and Zylon®
provide superior break-open protection.
Thermal Conductivity of FR Fibers
120
100
Thermal 80
Conductivity 60
[W/(m. K)] 40
20 0.04
0
100
0.04
0.25
15
Fiber
Decomposition Temperature
1300
1100
900
°F 700
500
300
100
COMFORT
Comfort and flexibilty of the outer shell are very important characteristics for the firefighter. When
fighting fires, the wearer should have the least amount of stress caused by the gear since stress is one
of the top causes of line-of-duty deaths. The comfort of a fabric can be related to the modulus and
moisture regain of the fiber.
Modulus
Grams/
Denier
Modulus – The fiber’s resistance to bending. Higher modulus fiber translates into a less flexible
fabric. High modulus means a stiff material.
DURABILITY
Durability of the outer shell is usually measured via tear and abrasion resistance. The tenacity of the
fiber characterizes strength. Note that the durability of the fabric can be affected by UV light. UV light
affects the performance of para-aramids and PBO fibers.
Tenacity – The higher the tenacity, the stronger the fiber. Since PBI is not a strong fiber, it’s blended
with para-aramids, e.g. Twaron® and DuPont™ Kevlar®, to provide strength in the fabric. An independent study* concluded that PBO’s tensile properties decreased more rapidly than those of p-aramid
fibers when exposed to UV.
Tear Resistance – The industry test commonly used is the trapezoidal tear, which measures the
pounds of force required to propagate a 1/3 inch tear in a fabric.
Tenacity
Grams/
Denier
UV Resistance
250
Tear 200
Strength 150
(lb)
100
50
0
0 oz. 35
PBI
PBO
(ZYLON )
®
• Advance Ultra®
Found in the • PBI Max
• Kombat Flex™ • Millenia™XT
following
• Agility™
outer shells: • PBI Matrix™
• Gemini XT
Introduced in
the fire service:
1984
Country of origin: USA
1999
Japan
0
60
120
180
Xenon Exposure (hr)
5
Did you know?
PBI fabrics have been used in the fire service for over 30 years and
continue to be used in other markets such as industrial/electrical,
aerospace, military, and motorsports.
Since its introduction in the late 1990s, Zylon® has been utilized in various
markets including the fire service, but has been discontinued in several
markets including military and police ballistics, sail cloths, and rope.
From the time PBI was introduced to NASA for the Apollo missions in
the late 1960s, it has been regarded as the best protection available for
high-heat and flame applications.
*Liu, X. and W. Yu. 2006. Degradation of PBO Fiber by Heat and Light. RJTA 10(1):26-32.
PBI Performance Products assumes no liability for the results or usage of these products. The technical data to the best of our knowledge is accurate at time of publication. This bulletin is subject to change pursuant to new developments and findings. A similar reservation applies to the properties of the products
described. Users of any product must satisfy themselves by independent investigation.