Potbelly, named after a stove that warmed the first store, raised $105 million in its initial public offering, the Chicago Tribune reported Saturday.
The Wall Street Journal said Potbelly considered starting prices between $9 and $11, then somewhere between $12 and $13, before taking an opening-day gamble at $14 per share.
Investors were hungrier than the company thought -- the share price peaked at $33.79 in mid-morning, before closing at $30.77, a gain of 120 percent on day one in its life as a public firm.
Noodles & Co. saw its shares double in June on its first trading day as a public company. Teavana Holdings Inc. shares climbed 64 percent on day one in July, the Journal said.
Potbelly started as part of an antiques store that opened in 1977 on Lincoln Avenue in Chicago.
Bryant Keil bought the business in 1996 and set out to expand the brand. He was chief executive officer until 2008, when he handed the reins to Aylwin Lewis, who used venture capital to expand the brand further.
The restaurant's success relies on toasted sandwiches, custom ordered, home-made cookies and a staff willing to engage in small talk with customers, the Journal said.
"Sandwiches are portable and customizable. You can dictate how many calories you intake with our product. It's a beautiful category to be in," Lewis said.