Superhero team-ups are all the rage these days, but one has to wonder how chummy those super-friends really are once the director yells cut.

The stars of Marvel's The Defenders swear they are thick as thieves; as proof, they offer up the most contemporary of friendship metrics - they group-text one another.

The series, which debuts on Netflix on Friday, unites the leads of the streaming platform's four superhero shows - Daredevil, Jessica Jones, Luke Cage and Iron Fist - as they face a new threat menacing New York City.

Alien actress Sigourney Weaver steps in to play an arch-villain who is somehow connected to The Hand, the mystical criminal cult the heroes have been battling individually.

In one-to-one chats with The Straits Times in New York recently, the four leads say that just as The Defenders will see their characters form a sort of support group for reluctant superheroes, they themselves have coalesced into a surrogate family since they all moved to New York to film their respective shows.

Krysten Ritter, who plays the titular tough-as-nails private detective in Jessica Jones (2015 to present), says of their chemistry: "Sometimes you get lightning in a bottle and people really get along, and sometimes you don't.

"We got lucky - all of us just got on like gangbusters. Can't get enough of one another. I mean, you can't even get us to stop talking to work," the 35-year-old says, giggling.

"The four Defenders have a really fun text chain, actually," says Charlie Cox, 34, who plays Matt Murdock, a blind crime-fighting lawyer, in Daredevil (2015 to present). "It's of great amusement," he says, revealing that Ritter recently texted a picture of herself wearing Daredevil-themed pyjamas.

Adds Finn Jones, who portrays martial arts expert Danny Rand in Iron Fist: "It's always a good day when we see one another again. We have a great dynamic - we get one another, we support one another.

"That doesn't always happen. There can be a lot of egos on set sometimes."

He sheepishly confesses that he and Cox - who are both British - "even live in the same building now, just by chance".

Cox, who has a nine-month-old daughter with his television producer girlfriend Samantha Thomas, even goes to him for decorating advice. "We're going around sharing tips for curtains. He's coming around to check mine out," says Jones, who is 29 and single. "We've become total housewives."

The closest bond seems to be between Ritter and Mike Colter, the 40-year-old who plays Harlem's hoodie-wearing hero Luke Cage (2016 to present).

The pair met at a "chemistry read" to test their suitability to play allies and love interests in Jessica Jones. Now, "Mike and I are like best girlfriends - we won't stop talking," says Ritter, who is dating guitarist Adam Granduciel, 38. "He makes me laugh so hard. We text all the time."

The friendship extends to Colter's wife, Iva, a 42-year-old Netflix talent executive, and the couple's two-year-old daughter. "I text with his wife all the time; I FaceTime with his daughter. We're really close friends, which is awesome," Ritter says.

"As you get older, you don't always make new friends in your 30s - not real friends. And I feel so lucky, I have all these new friends who I know, if I'm in a bind, I can call up and they'll be there."

Group therapy to create chemistry

The show's four stars also bonded over their similar professional trajectories, with each having scored the first big leading role of his or her career with these characters.

Jessica Jones, Luke Cage, Daredevil and Iron Fist have amassed large enough audiences that it is almost impossible for any of them to go unrecognised these days.

"My disguises don't work as well as they should," observes Colter. "I have a lot of hats. It gives me a second or two of anonymity."

The experience has been "100 per cent" life-altering, Ritter says.

"The fact that it's big and people watch it, and it's on a platform like Netflix that makes it global, people know you're Jessica Jones. That's the most life-changing thing - that people have watched it and like it."

Their characters' chemistry was carefully orchestrated. The trailers reveal the requisite superhero banter as the four get to know one another, and the actors say the characters will grow and learn from these interactions.

In fact, "group therapy" was Marvel's working title and the production team's nickname for the show, reveals Jones.

"And Danny gets a lot out of the group therapy. At the end of Iron Fist, he doesn't even know what a superhero is or how to handle this responsibility. In The Defenders, he meets these people who are using their abilities with purpose and drive. And Danny's really inspired. They help sharpen and focus him."

Still, Danny's initial approach causes trouble. "He's the reckless optimist - he's like the Scrappy- Doo of the group," says Jones, referring to the cartoon dog who is always spoiling for a fight. "He sees trouble and is, like, 'Right, guys, let's get 'em.' That can often get us into trouble."

Daredevil Matt, on the other hand, "is the sensible one and tries to be an older brother to Danny", says Cox. Jessica is typically the resident smart-ass, adds Ritter, while Luke "just hangs in the corner, looking cool, waiting for something to pop off - and then he'll break some faces", Colter says in jest.

The series' developers, Douglas Petrie and Marco Ramirez, had to take care to preserve each character's distinctive characteristics in these ensemble scenes.

Colter says: "We all switched roles from time to time - such as who is the voice of reason, who is saying something as a punchline, who is taking things a little more seriously. I think we were able to blend (it) so that we don't become archetypes.

"The hard part for Marco was making sure each character had representation, each fan base understood its character was being represented and each character had a clear voice and point of view.

"So when they debated, they could win their debates, even if it ended with them agreeing to disagree."

One of the more interesting exchanges takes place between Colter and Jones when Luke calls out Danny for being a privileged "billionaire white boy".

"It's not just about characters who come together and have a jolly old time and fight crime," Jones says. "Actually, there's a really good level of conversation about us coming from different backgrounds, and exploring that.

"That really grounds the relationships between us and makes the show even more interesting."

•Marvel's The Defenders starts streaming on Netflix on Friday.