Pope Francis poses for a selfie as he arrives at the San Giuseppe all'Aurelio parish in Rome for a pastoral visit, Dec. 14, 2014. Getty Images

Diana Orlandi, president of the Penn Catholic Student Association, wasn’t expecting much when she set up her organization’s table at the University of Pennsylvania’s activity fair last month. Maybe a few of her members would stop by, she thought, or some freshmen would join up.

But the life-size cardboard cutout of Pope Francis she put next to her table changed that. When students -- even upperclassmen -- spotted it, they walked over in droves. “People came and took selfies with him, came to talk to us,” said Orlandi, 21. “There were people we’d never seen before.”

Gone are the stuffy pontiffs of centuries past. The Twitter-using, evolution-embracing, pizza-loving Pope Francis now heads the Catholic Church, and in addition to shaking things up on everything from divorce to climate change, he has developed an unusual fan base among young people. Experts say Francis’ reputation for authenticity and literally practicing what he preaches has struck a chord with millennials -- a critical achievement, because they’ve been called the least religious generation in American history and could represent the future for the Catholic Church, which has lost as many as 3 million members in the U.S. since 2007.

“For many millennials, the idea of religion they've learned is about rules and admonitions and focused on things like abortion, same-sex marriage,” said Daniel Cox, research director for the Public Religion Research Institute, a nonprofit based in Washington. “Pope Francis really represents sort of a fresh take.”

Jorge Mario Bergoglio, an Argentinian Jesuit, was elected after Pope Benedict XVI resigned in February 2013. He chose the moniker Francis after St. Francis of Assisi, a man who lived most of his life on the streets as a poor evangelical, and as he distinguished himself from his predecessors he fell in line with his namesake. Francis visited the slums of Rome at night to give alms. He decided to stay in his two-room apartment and drives a used Ford Focus. On his first Holy Thursday, he washed the feet of Muslims and women.

Actions like those attracted Michael Fuentes, the 21-year-old president of the Catholic Student Association at the University of Miami in Florida. Francis is out there actually doing the things the Bible recommended and showing that he cares about everyone, Fuentes said. That’s what makes him cool.

“It’s genuine holiness -- you know he’s not trying to fake it,” he said, adding that young people appreciate transparency in public figures. Fuentes said Francis’ interest in helping the poor particularly appeals to college students who can relate to living paycheck to paycheck. It also helps put a face to and give a solid example of what Catholicism is all about.

"Honest is the word I keep coming back to," said Amy King, the 21-year-old president of the Catholic Student Association at Texas A&M University. "He's a good role model for anyone, Christian or not."

This attitude is important for youth, 35 percent of whom told Pew Research Center earlier this year that they had no religious affiliation. Because so many of them don’t have the religious background -- think Sunday school and weekly Mass -- of previous generations, what they see of Pope Francis in the news is often their first introduction to the church. That’s a lot of responsibility.

Francis needs to be relevant, approachable and compassionate so millennials see religion that way, as well, according to Robert McCarty, executive director of the National Federation for Catholic Youth Ministry, a nonprofit in Washington. And he’s succeeding. Pew found that Pope Francis' favorability among American Catholics of all ages was at 85 percent in 2014, an approval rating of a level not seen since Pope John Paul II.

"I think the pope is redefining faith and religion," McCarty said, adding that it's also important for local church communities to echo his messages. “Young people in the past saw the church as saying, 'This is what you have to believe.’ Francis is saying, ‘This is what you have to do.’ ”

It’s piqued the interest even of people who don’t consider themselves Catholic. Mariêad McCarron, a 20-year-old acting student at New York University who said her relationship with faith is “complicated,” sees Francis as a political figure. But she also said he represents the slow but steady modernization of the church. The pontiff can’t do too much to change things, but McCarron said she respects his willingness to tackle social issues, such as when he declared “who am I to judge?” gay people in April or when he announced priests could forgive abortions during the Holy Year.

"He's humble. Very humble," said Gianmarco Vitti, a 23-year-old student at New York University. "He goes out of his way to show people he's just like them, which I think is commendable."

But even though Pope Francis’ U.S. visit this week could further his cool factor, it’s still unclear whether it could inspire millennials to return to the church, said Cox. While roughly two-thirds of young people like the pontiff, only 48 percent have a favorable view of the Catholic Church as a whole. The task of bridging that gap falls largely to local parishes, he said.

“He's been on a baseball card now, there are pope emoji ... there are all these ways he's seeping into all these different aspects of American political and cultural life, and that’s new,” Cox said. “The challenge is how do you translate this transcendent popularity into commitment to the institutional church?"