What’s the trick to the Instagram-friendly jack-o'-lanterns in Fairmount Park? Molded foam.

As Halloween month hits its stride in Philly, thousands of hand-carved jack-o’-lanterns adorn West Fairmount Park for Jack’s Pumpkin Glow, a monthlong event that brings 5,000-plus pumpkins intricately carved into likenesses of Philadelphia’s most famous historical figures, as well as Disney princesses, Day of the Dead skulls, even dinosaurs.

For about $25 a pop ($17 for kids), attendees walk through the park over the course of 15 to 30 minutes, snapping shots of the illuminated displays — some from a distance and some close-up.

Near-identical iterations of Jack’s Pumpkin Glow take place in Washington D.C., Chicago, and Nashville; last year, it also visited Pittsburgh, Charlotte, N.C., and Boston (under the name Jack O’Lantern Journey). This year a similar series of events, Rise of the Jack O’Lanterns, set up shop in New York City, Long Island, North Jersey, and Westchester County, N.Y. The trend has spread to the West Coast, too, including Pomona, Los Angeles, and San Diego.

Key to pulling off national rain-or-shine spectacles that spotlight perishable produce: “Fumpkins,” or fake pumpkins made from molded foam, lit by LED lights.

Shannon Donnelly, vice president of Jack’s Pumpkin Glow, said that, over the course of the event, about 4,000 to 5,000 real pumpkins are carved on-site by a team of 15 carvers, who rotate them in and out as they decay. Six thousand fumpkins are constants — constituting more than half the pumpkins that attendees see on park lawns.

Understandably, this has left some attendees disappointed.

“None of the pumpkins are real on display, which was disappointing,” said Laurie McGarrity, who brought her kids to the event in Philly last year. “I thought it cost a lot for what it was. Cute, but one and done.”

“SCAM!!!,” read a recent Google review of Fairmount Park’s Glow event. “Everything is fake and it’s advertised as real hand carved pumpkins. They even have someone carving a pumpkin when you first walk in to make you think it’s all real. It’s definitely false advertising. They were all styrofoam.”

The false advertising complaints, as well as reports of overcrowding and difficulty parking, are echoed in other reviews of Philadelphia’s Glow, as well as those in Boston and near D.C., including one by a Washington Post reporter who said the precise, identical nature of the pumpkins made them “unintentionally creepy.”

But not all attendees are let down. Tamika Levels-Hood and her husband brought their 8-year-old daughter to the event in Fairmount Park for the first time last year. She said she couldn’t even tell that some pumpkins weren’t real.

“I don’t believe any novice would know any different,” said Levels-Hood, who lives in Pennsauken.

“It was an interesting experience,” said Michael Lee, who brought his kids from Center Valley to see the pumpkins on a recent Saturday night after seeing ads for the event on Facebook. “I thought the displays were fantastic and original. We would come back next year.”

Other attendees agreed, praising the event’s Philly touches, which included tributes to Robert Indiana’s LOVE and AMOR sculptures, carvings of Kevin Hart and Bradley Cooper, and a graveyard with tombstones for Tom Brady and Bill Belichick.

“I’ve never seen that many carved pumpkins in one space,” said Sean Fischer, who came with his family from South Jersey. “You can tell that there was thought put into it.”

Most of the fumpkins, which are used in the more intricate displays, are placed farther from the path that visitors walk on, while the real pumpkins are scattered next to the path.

In the months leading up to the show, staff members are in constant communication with local farmers about their pumpkins. “How many live pumpkins we get to use depends on the weather,” Donnelly said. “Sometimes they’re a little softer, which means they don’t last as long.”

But when guests are paying $25, organizers can’t call off the show because of a poor pumpkin crop.

Carvers work on fumpkin displays year-round. The displays are kept in storage until the event, and the most popular — like the dinosaurs — are reused year after year.

“When you consider that fumpkins allow this to turn into an art installation because it preserves the time that an artist spends carving a pumpkin, then it makes sense,” said Lindsay LoForte, a carving specialist with Jack’s Pumpkin Glow. “If I spend 20 hours carving a celebrity face into a pumpkin, it would be really great and efficient to see that again next year.”

Corinne Boyce attended the Jack O’Lantern Journey last fall in Boston’s Franklin Park Zoo, produced by the same company that oversaw the Glow in Philadelphia. She said that the pumpkins were “100% fake,” even though the event contacted her afterward to confirm that real pumpkins were present.

“They seemed like ones you would buy from the store, for sure,” Boyce said.

Boyce said she felt extra disappointed because, in previous years, she had attended the Jack-O-Lantern Spectacular at the Roger Williams Zoo in Providence, R.I., the original jack-o’-lantern event. The Spectacular was founded by the Reckner family in 1988 and runs for 33 nights, featuring a blend of around 5,000 hand-carved fumpkins and pumpkins.

“Anybody who tells you they’re doing a monthlong jack-o’-lantern event and they’re all real pumpkins is lying,” said Travis Reckner, president and CEO of Passion for Pumpkins, the company behind the Spectacular. “We used to do it in the early 2000s, when the event would only be a weekend, and we would have volunteers light candles in the jack-o’-lanterns by hand, but we would have to charge $50 to $100 to maintain costs.”

Reckner said that in the event’s current iteration, the company still uses a lot of real pumpkins, especially for the displays that are closest to the trail. The biggest, most ornate carvings at the Spectacular are all done on real pumpkins — Reckner has years-long relationships with giant pumpkin growers, who grow gourds that can weigh up to 1,000 pounds. Carving them takes 6 to 12 hours on average, and up to 40 in some cases. Reckner even hung real pumpkins in the trees until their insurance company stopped them.

Reckner said that the other thing event organizers must consider is that as the show goes on, the lifespans of the live pumpkins get shorter and shorter.

“When you put thousands of real pumpkins in the woods, you create a giant mold/fungus monster,” Reckner said. “The more fresh pumpkins you bring in, the bigger the monster gets.”

His solution? A slower expansion of the Spectacular allows Reckner to keep more live pumpkins in the show, to the delight of visitors.

“We’ve had so many venues that have asked us to come, but we can’t go because of quality control,” he said. “We’re creating a living organism that needs to be maintained and fed and kept alive.”