The Auxetic Effect

ypically, if a flexible material is stretched in one direction, it thins out in the
other; and if compressed in one direction, it thickens in the other. However, in the case of
auxetic materials, the converse is true. For example, if a thin, inelastic fiber is wrapped around
an elastic core and then pulled lengthwise, the elastic component bulges outwards. This simple,
elegant auxetic effect can be the basis of some revolutionary solutions for all sorts of textile

Zetix™ helical-auxetic fiber technology – developed in the United Kingdom by Dr. Patrick
Hook, managing director, Auxetix Ltd., in collaboration with researchers at the University of
Exeter and Dow Corning Ltd. – has won several awards, including the Techtextil 2007 Innovation
Prize. Hook, an engineer who had been involved in the motor racing arena prior to pursuing a
doctorate in engineering with a focus on auxetic materials, established Auxetix to commercialize
the patented technology. Auxetix now has granted an exclusive license to Houston-based Advanced
Fabric Technologies LLC (AFT) to develop and market Zetix fabrics for use in blast-mitigation and
ballistic-protection fabrics in North America, as well as first right of refusal to market and
manufacture the fabrics elsewhere in the world.


A test conducted by the UK Ministry of Defence compares the performance of a Zetix™ blast
curtain (left) with that of a conventional blast curtain.

“This is a completely new approach to material science, particularly for blast and ballistic
mitigation, and we think it’s going to be a game-changing, breakthrough technology,” said Tony
Lentini, AFT’s vice president of marketing.

Zetix comprises a series of auxetic yarns, each yarn wrapped using S or Z twist with a
high-strength cord — or “power thread,” as Lentini described it — and woven by weft insertion
across the warp. Off the loom, the weft becomes the tensile element in the fabric. “When force is
applied,” Hook explained, “the auxetic yarns deform, opening thousands of small pores in the
fabric’s surface. In so doing, they absorb the peak pressures from the blast wave and yet allow the
rest to pass through. At the same time, they catch any airborne debris such as glass shards,
shrapnel or secondary fragmentation.” In simulated car bomb testing and grenade testing, Zetix has
shown “remarkable resilience,” sustaining negligible damage after eight nearby grenade blasts, he

“It is the only material on the market that automatically adjusts its strength and thickness
in response to explosive forces,” said AFT CEO David O’Keefe. “Because it has memory, it returns to
its neutral state when the stress is dissipated.”

The basic Zetix fabric is made with a Spectra®-wrapped polyester monofilament and ballistic
nylon; but materials such as Kevlar®, Vectran™, Hytrel®, Nomex®, fiber optics or telemetric
materials may be used for specialized applications.

“That gives you the capability to have many generations of Zetix,” O’Keefe said. “We can
immediately increase the strength by probably 80 to 85 percent just by substituting Vectran for
ballistic nylon.”


Bungee cords wrapped with inelastic cords and then stretched demonstrate the principles of
helical-auxetic technology.

Potential blast- and ballistic-protection applications include spall liners for armored
vehicles, allowing a reduction in armor thickness and a consequent reduction in vehicle weight.
Incorporating Zetix in body armor worn by soldiers in the field also could lighten the load they
must bear.

O’Keefe said Zetix will be cost-competitive weight-for-weight with other blast-mitigation
fabrics, and its performance advantage will provide added value. “Because it’s not a single-event
fabric, the cost of development or installation would be recouped pretty easily,” he said.

Although Zetix has successfully undergone official testing in the United Kingdom, the
performance data from those tests is not easily accessible, so AFT is conducting testing in the
United States so it can provide specific results to potential users. “We want to provide hard data
to support Zetix’s claims, and we’re working with other companies and independent testing labs to
generate it,” Lentini said.

AFT is working with US and Canadian manufacturers including Greensboro, N.C.-based BGF
Industries Inc. and Quebec-based JB Martin Co. to produce Zetix fabric and is seeking additional
partners along the supply chain for various aspects of production.

“We’re looking for materials that would work well and be low-cost, and we’re looking for a
variety of sources,” Lentini said. “For example, a critical component is the wrapping of the power
thread because it’s key to the whole auxetic effect. We’re looking for people with capabilities to
do that efficiently and who can supply that thread to the weavers.”

Virtually Unlimited Potential

While the immediate focus for Auxetix and AFT is to provide blast-mitigation and
ballistic-protection solutions for military and first-responder applications, there are many other
areas in which Zetix technology can play a role. Even those initial solutions have relevance for
non-defense applications, such as mine safety, hurricane protection, satellite testing, jet engine
shielding — the list goes on. Nomex or a Hytrel flame-retardant yarn could be incorporated to add
protection from high-heat or a fireball. With the addition of fiber optics, a Zetix apparel fabric
could change color to help camouflage the wearer; or the addition of telemetric materials could
allow remote monitoring of a person’s heartbeat or other vital signs. In the medical field,
potential applications include adjustable bandages, sutures and medication delivery. There is good
potential for filtration, as the behavior of the yarns can allow a filter to self-adjust in
response to applied force; and the self-adjusting capability in a seat belt could help minimize
injury from an accident.

“Down the road, your imagination is the only limit to what this might do,” Lentini said.
“Way down the road, imagine a military battle uniform that is blast- and shrapnel-resistant, can
change color because of fiber optics, has telemetry that will measure a soldier’s vital signs and
could send a signal to adjust a built-in tourniquet. This may be pie in the sky now, but the
auxetic effect is so important here, you can let your imagination run wild.”

For more information about Zetix™, contact David O’Keefe 1-281-872-7272;;

May/June 2010