Shoe maker Allbirds’ shares surged 90% in their market debut on Wednesday, as the company nabbed a valuation of roughly $4.1 billion.

The company, known for its eco-friendly wool sneakers and slip-ons, opened its first trade at $21.21, after pricing 20.2 million shares a day earlier at $15 apiece, and raising roughly $303 million. Allbirds had marketed 19.2 million shares priced between $12 and $14, ahead of the initial public offering.

Shares closed the day at $28.64 apiece, up nearly 91%. The company is now listed on the Nasdaq exchange under the ticker symbol “BIRD.”

In going public, Allbirds is hoping to attract investors who favor companies that put an emphasis on sustainability.

“We did get exposure to a lot more pockets of capital as a result of the fact that people saw the genuine and authentic leadership that we’re putting forward on ESG,” co-founder and co-CEO Joey Zwillinger said in an interview on CNBC’s “Squawk Box.” “I think why the demand was so great … investors were really attracted by the opportunity to put their capital against great opportunity to create outcomes that were better for the planet.”

The listing follows the public debut of eyeglasses maker Warby Parker, the IPO of outdoor goods seller Solo Brands and that of fashion rental platform Rent the Runway. It adds to the wave of trendy, venture-backed retailers testing investors’ appetite on Wall Street.

When asked what would be a fair comparable for Allbirds’ business, Zwillinger said it’s a mix between traditional retailers with lots of stores and internet savvy brands. Allbirds counted just 27 brick-and-mortar locations as of the summer, but it’s planning to ramp up that number by the hundreds.

“It’s tricky. My business is in making fantastic shoes and selling to customers and creating great experiences,” he said. “The financial part, we’ll let the investors drive the way.”

Allbirds is hoping to cash in on an uptick in demand, especially among younger shoppers, for products that are comfortable and also sustainably sourced. It recently launched an activewear line, expanding its product assortment beyond its popular wool sneakers. It also sells socks and other accessories.

According to Zwillinger, customers who have long shopped at Allbirds for footwear are now stocking up on other items and growing the size of their baskets.

“We’ve been really focused on pegging people who come to know and love us because of our shoes,” he told CNBC in a separate phone interview. “And because they understand that we take these naturally derived materials to make incredibly comfortable shoes and we can take that same information and put it into apparel.”

But the company has yet to turn a profit, which could worry potential investors.

Allbirds’ net loss totaled $14.5 million in 2019 and grew to $25.9 million in 2020, according to documents filed with the Securities and Exchange Commission.

And it expects to book a net loss of between $15 million and $18 million for the three-month period ended Sept. 30, compared with a loss of $7 million a year earlier.

“Before the pandemic, we were already very close to and on the path to breakeven,” Zwillinger said. “So this is something well within our sights, and we see a very clear and short-term path or else we wouldn’t be going public.”

Opening more stores in the United States and overseas should help to boost profitability, he said.

Morgan Stanley, J.P. Morgan and BofA Securities are the lead underwriters for Allbirds’ offering.