Nomex®

Last updated: August 27, 2009.

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 used for!

Photo: A pair of Nomex gloves like these could make nasty oven burns a thing of the past.

What is Nomex?

Photo: Turn Nomex gloves inside out and you can see how thickly woven they are. They're like a pair of thick woollen gloves, but wool alone could never give such amazing heat protection.

Nomex is the friendly brand name for a heat- and flame-resistant textile made by the DuPont™ chemical company. Technically, it's called a synthetic aromatic polyamide polymer—which sounds complex but starts to make more sense if you consider it one word at a time:

• Synthetic textiles are made in a chemical laboratory (unlike natural textiles such as cotton, which grows on plants, and wool, which comes from animals).
• Aromatic means its molecules have a strong, ring-like structure not unlike that of benzene.
• Polyamide means the ring-like aromatic molecules connect together to form long chains. These run inside (and parallel to) the fibers of Nomex a bit like the steel bars in reinforced concrete.
• Polymer means that Nomex is made from many identical molecules bonded together (each one of which is called a monomer). Plastics are the most familiar polymers in our world. As we've seen, the monomers in Nomex are based on a modified, benzene-like ring syructure.

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.

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 form.

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.

Photo: These gloves are made from Nomex III, which is roughly 95 percent Nomex, 5 percent Kevlar, and a little carbon fiber to reduce static.

What's so good about Nomex?

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.

The tough, woven structure of Nomex is extremely strong, has high heat resistance, is flame retardant (it doesn't melt or drip) 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.

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. On the right, a chair made from fire-retardant fabric burns much slower. Often the fire goes out before too much damage is done.