Four years ago, a classic yellow school bus gave online eyewear company Warby Parker the confidence to open brick-and-mortar stores. On Friday the bus returned to town enabling Warby to sell eyewear in the park across from the Philadelphia Museum of Art.

A half-dozen people had climbed aboard the Warby Parker Class Trip bus at Eakins Oval just before 1 p.m. to try on glasses, with an optician on hand to take measurements and write prescriptions.

Marielle MacMinn, 27, of South Philadelphia, who will start law school next month at Temple University, was trying on a new pair of specs, starting at $95.

She gave her order to Warby employee Jon DeMone, choosing Finch striped-molasses glasses and spending $30 more for a thinner and lighter frame.

"I'm very excited. I love them," she said. "What I really like about [Warby] is they give a pair of glasses to communities in need" for every purchase, she added.

The old school bus - the retail equivalent of a pop-up bar - will be selling eyewear through Aug. 21 at the oval. It shows how hot retailers are using all available means - from apps to staged events to traditional storefronts - to sell their wares.

"We're in an age where the pressures on large, bricks-and-mortar retailers has made them extremely cautious, leading to homogeneous and boring stores," said Garrick Brown, vice president of retail research for the Americas at Cushman & Wakefield. "These upstarts, including Warby Parker, take chances, have interesting goods and outside-the-box merchandising, and are simply interesting."

Warby Parker was launched in 2010 by four Wharton School grads.

Six years later, Warby Parker has 31 stores - seven smaller showrooms, including one in Old City, and 24 retail stores in Chicago, Los Angeles, San Francisco, and other cities.

Warby will open a store this year on the site of the former Le Bec-Fin restaurant at 1523 Walnut St.

Larry Steinberg, an executive vice president at CBRE Inc. who negotiated the Warby deal in Center City, said the retailer and others like it are replacing the luxury retailers that left with lower prices and "a high-fashion component."

"They are increasing their street presence to capture that segment of the market that needs instant shopping gratification, the same reason that other online retailers, like Bonobos, have made the move," he said.

Warby cofounder and co-CEO Dave Gilboa said the company fills a need.

"In 2010, you could go online and buy a lot of consumer products, but not glasses," he said.

So Gilboa and three fellow M.B.A. students, Neil Blumenthal, Andrew Hunt, and Jeffrey Raider, hatched a plan. They invited customers to Blumenthal's apartment at 22nd Street and Delancey Place in Center City to try on frames in person.

"We laid out glasses on the dining table . . . and loved the experience," Gilboa, now 35, recalled. "We learned a lot about product design and marketing."

After graduating from Wharton in spring 2010, the foursome leased a few hundred square feet in a New York office to run Warby Parker.

They later tested pop-up shops in the city. In October 2012, the Warby Parker Class Trip hit the road, visiting 16 cities in just over 15 months.

"We found out which cities were the most receptive" for opening stores, said Gilboa, who shares the co-founder/co-CEO title with Blumenthal. Hunt and Raider are cofounders. "It gave us the confidence to sign permanent leases."

In April 2013, the first Warby Parker store opened in Soho in Manhattan at 2,000 square feet and became an instant hit.

The privately held company does not disclose sales. Online commerce remains the bulk of sales and is funding the expansion, Gilboa said.

Customers can order up to five Warby frames online and have them shipped. They have up to five days before they have to ship the frames back using a free shipping label, along with their order and prescription.

For every pair of Warby glasses sold at retail, the firm donates a second pair to the third world via a nonprofit group.

"Our goal was to dramatically bring down the price of glasses and do some good for the world," Gilboa said. "We also make the shopping experience fun."

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