There’s talking green and then there’s being green, and Chip Bergh, CEO of Levi’s Strauss, knows how to do both.

In a recent interview at Fortune’s Brainstorm Green conference in Laguna Niguel, Calif., Bergh talked about the efforts he has made as CEO in the last few years at Levi’s to make the company’s products greener and more sustainable—environmentally, economically and socially.

In a time when “fast” or “throwaway” fashion is common, Bergh boasts about the quality of Levi’s products, mentioning that May 20 marked the 141st birthday of the classic Levi’s 501 jean and that Levi’s also is the number one brand in secondhand clothing stores.

“We are the ultimate in sustainable apparel,” Bergh says in the interview. “If you buy [Levi’s jeans] they will last a lot longer than most people’s waistlines will.”
So, what is it that makes Levi’s jeans so durable and sustainable exactly? Bergh will tell you that it’s the hard work and research that goes into making their products, but he also has one secret tip to offer—one that he says has worked beautifully for him.

“These jeans have yet to see a washing machine,” Bergh said of the jeans he wore during the interview, a pair he said he’s owned for a whole year.

I have yet to get a skin disease.”

Levi’s is set to launch their new “Water<Less” line of products in collaboration with Water.org, which the company claims to use 96% less water to make.