Innovative Lives

Stephanie Kwolek
and Kevlar®, The Wonder Fiber

by Caitlyn Howell

Kevlar, The Wonder Fiber
KwolekImagine this. It is 1964. You are a chemist working in a research laboratory of a major company. Your boss has asked you to find new synthetic polymers. You spend some of your time experimenting with the polymers you and your coworkers have already made, while other times you are busy combining, heating, stirring, and spinning different substances to see what you can create. Because you studied chemistry in college, and because you have worked in this laboratory for a few years, you know your stuff and have fun working with the other chemists.

One day, you combine some substances and heat up your mixture carefully, just as you do every day. But this day, something strange happens. The mixture is cloudy instead of clear. When you stir it, it doesn't look the way you expect. Something clicks in your head, and you rush to find the person in charge of testing new polymers. He isn't at all sure he wants to test this strange glop, but, after talking to him for a long time, you convince him. You're just sure there is something unusual about the substance in your test tube. You are right. When they hear the results of the tests, your colleagues run into your lab, excited and amazed. You have just invented a brand new polymer that weighs very little but is strong and stiff beyond anyone's imagination. A few years later, your discovery is used to make bullet-resistant vests and helmets. Your name and picture are in advertisements and billboards as the woman who saved thousands of lives.

The Making of a Chemist

In March 1996, Stephanie Kwolek shared her experiences with middle school students in one of the Lemelson Center's Innovative Lives programs."I did not start out to be a chemist. As a child, I thought that I might be a fashion designer. I spent an awful lot of time drawing various types of clothes and sewing," remembers Kwolek, the famous chemist in the previous story. Kwolek loved being outside as much as inside. She spent hours exploring the woods and creeks around her home with her brothers. Her father, who died when she was young, encouraged her to learn about nature by this first-hand experience. In school, Kwolek enjoyed her science and math classes. Her teachers encouraged her, helping her be a good student and talking to her about careers in science and chemistry. All of this was news to Kwolek, who had never heard of chemists or professional scientists. In high school, she decided she wanted to have a career in medicine, which meant going to college and then to medical school. As she explains, "I was always interested in science and mathematics. It was only natural I would go into some form of science."

Kwolek went to a women's college that was part of a much larger, all-men's university, as was common in those days (Today, the two colleges are both part of the co-ed Carnegie Mellon University.) She liked meeting professors and fellow students who were women interested in science; she also took some courses in the men's college. After majoring in chemistry, Kwolek was still absolutely convinced she wanted to go to medical school. But, she had to make money in order to fulfill her dream. So, she interviewed for jobs at several research companies, including the DuPont company. The interviewer from DuPont told her she would know whether she got the job in a few weeks. Kwolek remembers this conversation: "I decided to be very bold, and I said, 'I wonder if you could tell me sooner, because I have some companies requesting that I give them an answer whether I will accept their offers or not.' And this was true!" On the spot, she got the job.

Kwolek loved her job in the Textile Lab at DuPont. "The first year, the work was so interesting and it was so challenging. I loved to solve problems, and it was a constant learning process. Each day there was something new, a new challenge, and I loved that." In fact, she says, "the problem was that I was so interested in chemistry and research that I totally forgot about medicine." While she had assumed she would work only for a few years until she could go to medical school, much to her surprise she ended up staying at DuPont until she retired.

A Discovery!

Kwolek learned how to make long molecules called polymers that can be made into fabric or plastics. In 1964, her supervisor asked Kwolek and her coworkers to search for high-performance fibers. "At that time, we were already thinking about strong and stiff fibers, and one of the reasons why we were thinking in that direction was we had already seen that there was the possibility of a gas shortage. Now, if you could reinforce tires with a textile-type of fiber, which is lightweight, rather than steel wire, which is very heavy, you could use much less gasoline to operate the cars or airplanes or whatever other vehicles." Research chemists were also looking for fibers that wouldn't melt at very high temperatures, so that they could be used safely for objects that might get very hot or be exposed to such conditions.

During a typical day, Kwolek would combine substances to make a polymer, melt the polymer into a liquid, and ask a coworker to spin the liquid in a machine called a spineret. The spineret turned the liquid into fibers. Then, other scientists would test the fibers to see how much they weighed, how strong they were, and whether they stretched or broke easily.

Kwolek discusses her careerOne day, Kwolek was experimenting with two polymers that just wouldn't melt. She had to find a solvent that would dissolve the polymers into a liquid, instead of melting them. But something unexpected happened when she mixed one of the polymers and the solvent. She tells the story: "And one day, after many, many tries, I dissolved the polymer. But the solution was unlike any other polymer solution we had seen in the laboratory. Ordinarily, when you have a polymer solution of a flexible polymer chain, it sort of reminds you of molasses. It may not be as thick but is generally of a transparent or transluscent nature. With the polymer solution that I had, it was almost like water, and it was cloudy." When she stirred the solution, it separated into two layers: one yellow and clear, and one opalescent and cloudy.

Curious, she took the solution to the man in charge of the spineret. As she remembers, "he said to me, 'this will never spin, it flows like water. And, furthermore, it has particles in it and these will plug up the holes of the spinneret.' Well, previous to talking to him, I had filtered the solution....and there was no separation-the whole thing went through. I was convinced this solution would spin, because it just had the right flow and cohesive properties." After several days arguing with the man, "I wore him down," Kwolek laughs. "He said he would spin it. So we spun it and it spun beautifully," she says with a big smile. "I pulled on the fibers and they didn't fall apart, so I took them down to the physical test lab. We had them measured for strength and stiffness. A few days later, the results came back and I was really amazed. It was a very strong fiber, but the thing that really amazed me was the stiffness." And, when she baked the fiber, it became even stiffer. Kwolek had discovered a new fiber, called an aramid fiber, and a new type of substance, called liquid crystalline solutions.

Stephanie Kwolek is still amazed at her discovery, saying, "I knew the direction in which to go, but I will tell you this: I never expected to get the properties I did the first time I spun it." Her discovery was, she says, "a case of serendipity."

It Takes A Team To Go From Fiber to Store

Kwolek is quick to point out that many people work together to make new products, like aramid fibers. When Kwolek announced the test results, "everyone got very excited. We got together a group of people and we decided then there was commercial potential there, and the thing we had to do was find the right fiber for commercialization. Everybody got into the act, and it proved to be a very exciting, and sometimes frustrating, time." Some people were in charge of thinking up names (like Kevlar®), while others worked busily on submitting patent applications. There were chemists experimenting with similar liquid crystalline solutions, scientists thinking of ways to use and sell these superfibers, and others inventing new ways to spin these superfibers as well as stronger testing and cutting machines. Kwolek explains that "it turned out to be a great team effort in the end." And, Kwolek remembers lots of hard work: "Every day, there are highs and lows, there are times when you think the whole thing will sink because of all the problems that develop." Going from a discovery to a product that can be sold (product development) is a long process. It took ten years between the time Kwolek first stirred that test tube (1965) to the time bullet-resistant vests made with Kevlar® were available for sale (1975).

Kwolek and a few Kevlar productsToday, aramid fibers are used to make: boat hulls, bullet-resistant vests, coats, and dress shirts, cut-resistant gloves, fiber-optic cables, firefighters' suits, fuel hoses, helmets, lumberjacks' suits, parts of airplanes, radial tires, special ropes, pieces of spacecraft, some kinds of bicycles, tennis rackets, canoes, and skis. Aramid fibers are stronger and lighter than steel. A vest made out of seven layers of aramid fibers weighs 2.5 pounds, but it can deflect a knife blade and stop a .38-caliber bullet shot from 10 feet away.

Kwolek continued creating and experimenting with synthetic fibers. She never regretted sticking with chemistry instead of going to medical school. Although she never imagined she would grow up to be an inventor, she explains that "when you go to work for a comapny that does chemical research, one of the expectations is to invent things and particularly to invent things the company is interested in. So, eventually, you do invent something if you are interested enough and if you work hard enough. I was thrilled when I discovered liquid crystalline solutions." Still, she believes that "it takes a certain amount of luck, it takes being at the right place at the right time, because you may make an invention but no one may be interested in it at the time."

Stephanie Kwolek is proud that her invention has saved thousands of lives and is pleased that her lifetime of work on synthetic polymers earned her a place in the National Inventors Hall of Fame (in Akron, Ohio). Today she takes time off from her hobbies, sewing and gardening, to lecture about her life and invention. She is proof that a love of science can lead you in unexpected directions that might even include world-changing inventions! To students, Kwolek says, "Every person has value, no matter what you do. This is what you have to remember."

What kinds of questions did middle school students ask Kwolek? »

What's it like to be a woman inventor and scientist? »


Anne L. Macdonald, Feminine Ingenuity: How Women Inventors Changed America (New York: Ballantine Books, 1992).
Ellen H. Showell and Fred M.B. Amram, From Indian Corn to Outer Space: Women Invent in America (Peterborough, NH: Cobblestone Publishing, Inc., 1995)
Ethlie Ann Vare and Greg Ptacek, Mothers of Invention: From the Bra to the Bomb, Forgotten Women and Their Unforgettable Ideas (New York: William Morrow and Co., 1987)

Interested in women inventors? Read more about them!

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All text and images © Smithsonian Institution. Updated 3 March 2005.

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