by Chris Woodford. Last updated: May 25, 2015.
It's a racing driver's worst nightmare.
You come down the straight at over 200mph (300 kph), a tire blows out,
and you skid off into the crash barrier. You survive the crash but the energy
of the impact generates enough heat to make your fuel tank explode. Suddenly, the car
that could have carried you to victory has turned into a fireball. You
manage to escape, but now there's another terrifying threat: your
overalls catch fire! Fortunately, you're wearing an inner body-suit
made of an amazing flame-resistant material called Nomex®. So, as
you pelt from the car, the fire goes out all by itself. Shaken but
unharmed, you owe your life to an piece of amazing chemical technology. Let's
take a closer look at how Nomex works and some of the other things it can be
Photo: A soldier puts on a Nomex® hood and a flameproof suit. Photo by Ryan C. Matson courtesy of US Army.
What is Nomex?
Photo: A pair of Nomex® gloves like these could make nasty oven burns a thing of the past.
Nomex® is the brand name for a heat- and flame-resistant textile made by the DuPont™ chemical company. Technically, it's called a synthetic aromatic polyamide polymer, but let's not get bogged down with jargon. What does that really mean:
- Synthetic means made in a chemistry lab. Synthetic textiles (such as polyester, nylon, and so on) are artificial, human-made chemicals cooked up by chemists; they're the opposite of natural fibers such as wool (from animals) and cotton (from plants).
- Aromatic means the molecules in nomex are based on connected rings of atoms rather than straight-line branched structures.
- Polyamide means lots of molecules are connected together into chains. In chemistry, "poly" really just means "many," so polyamide means "many amide."
- Polymer is the proper chemical term for a plastic. It usually means a giant molecule made from many ("poly-") repetitions of a basic unit called a monomer ("-mer").
In short, what we have in Nomex is a man-made textile whose
ring-like monomers are bonded together into tough, long chains to make
immensely strong fibers. Break Nomex up and sort it into its atoms and you'd have
four neat piles of carbon hydrogen, oxygen, and nitrogen.
Photo: Left: Turn Nomex gloves inside out and you can see how very thickly woven they are. Although they look much like ordinary woollen gloves, wool alone could never give such amazing heat protection. Right: Inspect the label carefully and you'll see this is actually Nomex III, which is roughly 95 percent Nomex, 5 percent Kevlar, and a little carbon fiber to reduce static.
Aromatic polyamides such as Nomex are often
called aramids for short.
Kevlar® (another DuPont textile)
is also an aramid, but with a slightly different
chemical structure. If you're interested, the full chemical name of
Nomex is poly (m-phenylenediamine isophthalamide), while Kevlar is poly
(p-phenylenediamine terephthalamide); Nomex is a meta-aramid polymer
while Kevlar is a para-aramid polymer.
Aramids are made in a two-stage process. First, the basic polymer is
made by reacting together organic (carbon-based) substances to form a
liquid. In the second stage, the liquid is spun out to make solid
fibers, which can then be woven into textiles or converted into sheet
Nomex generally comes in three kinds. It's either used by itself (as
100 percent Nomex), blended with up to 60 percent Kevlar, or blended
with Kevlar and some
anti-static fibers. In this last form,
it's known as Nomex III.
What makes Nomex fireproof?
Two superb properties of Nomex make it a perfect
protective material for race-car
drivers. Although Nomex burns when you hold a flame
up to it, it stops burning as soon as the heat source is removed.
In other words, it is inherently flame resistant. Just as important, the
thick woven structure of synthetic fibers is a very poor conductor of
heat. It takes time for heat to travel through Nomex; hopefully by that
time, you're away from the flames and out of danger. In the original Nomex
patent, five samples of the material were compared with five similar samples of cotton
(the control) in a basic flame test. The cotton samples caught fire in just 2 seconds and burned for 13–430
seconds; the Nomex ignited much more slowly (after about 4 seconds) and stopped burning after a mere 5 seconds when
the flame was removed.
Apart from high heat resistance and flame retardance (it doesn't melt or drip),
the tough, woven structure of Nomex is extremely strong and doesn't react with water.
What is Nomex used for?
Photo: Ready for battle: soldiers put on body
armor made from Kevlar and Nomex and used by explosives experts.
Photo by courtesy of US Army and Defense Visual Information Center.
Nomex is best known as a barrier to fire and heat. Apart from
race-car drivers, it's worn by astronauts, fire-fighters, and military
personnel. It's also widely used in more mundane ways, such as in my
household oven gloves. In sheet form, heatproof Nomex finds many uses in automobiles,
including high-temperature hoses and insulation for spark plugs.
But Nomex isn't just useful for protective clothing. The molecular
structure that stops heat passing through stops electricity flowing
through it as well. That means Nomex is an extremely poor
conductor—almost a perfect insulator, in fact. Nomex, made into the
form of a paper sheet or board, is a superb insulating material for all
kinds of electrical equipment, from motors
and generators to transformers and
other electrical equipment. For these applications, Nomex is often laminated
with Mylar® (polyester film) to make a stronger, tougher insulating material
that works at high temperatures without the individual layers coming apart.
Two-ply Nomex-Mylar laminate is called NM; three-ply is known as NMN
(where the Nomex goes either side of the Mylar); and four ply is NMNM.
Like Kevlar, Nomex is both very strong and very light, so it's often
used in aerospace applications. Nomex sheet is widely used to make the
honeycomb reinforcement inside helicopter
blades and airplane tail fins.
Photo: Nomex isn't the only fire-retardant fabric. Textiles used to cover chairs are often made from fire-resistant polyesters and other materials. This simple demonstration in Think Tank (the science museum in Birmingham, England) shows very clearly how fabrics like these can save lives. On the left, we have a chair made from ordinary fabric. A cigarette or match burn sets the fabric alight very quickly and gives off toxic fumes. Had this fire been left to burn, the whole chair (and the rest of the room) would have been completely destroyed. On the right, a chair made from fire-retardant fabric burns much slower. Often the fire goes out before too much damage is done.
Who invented Nomex?
The credit for this excellent invention goes to Dr Wilfred Sweeny (1926–2011), a Scottish-born scientist working at the world-famous DuPont laboratory in Wilmington, Delaware that also spawned nylon and Kevlar. While researching polymers, he developed one with with particularly good thermal properties that could be woven into a very tough fiber. Since Nomex was introduced in 1967, it has saved the lives of countless firefighters, pilots, soldiers, industrial workers—and, of course, racing drivers!
Find out more
On this website
- Preparative Methods of Polymer Chemistry by Wayne Richard Sorenson, Wilfred Sweeny, and Tod W. Campbell. Wiley Interscience, 2001. One of the definitive books about polymer technology, suitable for undergraduate and graduate students and professional chemists. (Wilfred Sweeny, the inventor of Nomex, is one of the authors.)
- Enough for One Lifetime: Wallace Carothers, Inventor of Nylon by Matthew Hermes. American Chemical Society/Chemical Heritage Foundation, 1996. Covers how nylon was invented—and the tragic story of the chemist who made the breakthrough.
- Nylon: The Story of a Fashion Revolution by Susannah Handley. Johns Hopkins University Press, 1999. Not about Nomex, but definitely of interest to anyone studying the impact of synthetic polymers on everyday life.
If you liked this article...
You might like my new book, Atoms Under the Floorboards: The Surprising Science Hidden in Your Home, published worldwide by Bloomsbury.