Four years later, Kullman is taking on a new challenge at a very different kind of company. The former Fortune 500 CEO will become president and chief executive of six-year-old 3D-printing startup Carbon, where she has served on the board of directors since 2016. It’s an unusual move for a ex-Fortune 500 chief, and especially for one of the few women to hold that role. Of 126 women who fell off Fortune‘s annual Most Powerful Women rankings—which include chiefs of the biggest companies alongside women in other corporate roles—between 2000 and 2015, only eight in 2015 had gone on to hold the CEO title at a private or public company of any size. Only two female Fortune 500 chiefs, Meg Whitman and Susan Cameron, in 2015 had ever repeated the feat at a second company. Kullman was the first woman to lead 212-year-old DuPont.

After rising to the top, a second tour is hard to come by. (Not so for men: of the 93 men during the same period who left their jobs under pressure, five of them later returned as CEOs of another public company). Kullman is excited about the venture, where she’ll head a workforce of about 500 rather than the more than 40,000 she oversaw at DuPont. “A non-public company is definitely more fun than a public company,” she says. “It’s different—yes, it’s a small team—but, boy, can you see the impact.”

Kullman takes over from Carbon co-founder and CEO Joseph DeSimone, who will become executive chairman. “Having a seasoned executive like Ellen [take over]—holy smokes, when this thought emerged, I couldn’t imagine something like this would come to fruition,” DeSimone says.

Since leaving DuPont, Kullman has served on the boards of Amgen, Dell Technologies, Goldman Sachs, United Technologies, and Carbon. Kullman, who has also advocated for women’s representation on boards of directors, says she will likely scale back some of her board commitments as she takes over the company.

Kullman said she had some hesitations before taking over the company: namely, moving from the East Coast to the West Coast and starting another full-time gig. Her goals for Carbon, however, are now clear: to use her expertise from DuPont to “deliver on the promise and mission of digital manufacturing.”

More must-read stories from Fortune:

—Female founders and employees are facing a gender equity gap
—J.C. Penney’s retail lab is at the center of CEO Jill Soltau’s turnaround plans
—Can virtual reality teach executives what it feels like to be excluded?
—The centuries-old frustrations of motherhood
—Microsoft reveals its gender diversity gap between workers and management
Keep up with the world’s most powerful women with The Broadsheet newsletter.