“I wasn’t interested in doing this in a studio, I wanted to do it in real places,” says Hany Abu-Assad, the Dutch-Palestinian filmmaker making his English-language debut with the movie.

The film was shot in sub-zero temperatures in the mountains on the border between the Canadian provinces of Alberta and British Columbia, the cast and crew flown in by helicopter.

“It’s so cold that even your eyes, when tears come, they can almost freeze and you can’t open your eyes,” says Abu-Assad, safely ensconced in a warm London hotel for this interview. “Even the hair inside your nose freezes and becomes very painful. But then you need fearless actors with you; you can’t do it alone.”

Donnie Yen talks about gangster epic Chasing the Dragon and reuniting with Wong Jing for Enter the Fat Dragon

Fortunately, Abu-Assad had a resolute Winslet, who – albeit 20 years ago – survived the experience of filming James Cameron’s Titanic. As soon as she took the role, she called her Titanic co-star Leonardo DiCaprio, who had also endured harsh conditions filming The Revenant.

“I did say to Leo, ‘OK, really how cold was it? I really need the proper inside scoop here’,” says the 41- year-old actress. It didn’t hurt that The Mountain Between Us shared a lot of its crew with those from The Revenant. “They knew what to warn us of, and how to be prepared.”

Like a mother on the mountain, Winslet – who has three children of her own – would make sure everyone else was safe and secure. “I would make chicken soup; I’d take one for me and one for Idris up the mountain.”

She also shared around a pair of battery-operated gloves – a present from her husband, Ned. “If somebody was losing their fingers, they became the emergency gloves,” she says.

Filmed chronologically, the mountain section took a month to shoot – with the team only able to endure six hours a day, half the usual shoot time. “That six hours felt more tiring than 16 hours [on the ground],” says Abu-Assad.

“It’s cold! You are hungry, because you don’t have catering up there. You don’t have toilets. You can’t go to the toilet anytime you want. You have to find somewhere. You don’t want to even go to the toilet because the moment anything … well, it’s so cold, if you take off your gloves, it freezes immediately.”

Winslet launches into a detailed analysis of the difficulties of performing bodily functions up on a mountainside. “You get in there,” she says with glee, “and before you take your gloves off, you arrange the toilet tissue [on the seat to prevent being frozen to the rim] and then you quickly take off one glove to undo your button and your zipper, and then the glove goes back on, and then it’s as quick as you can!”

With The Tag-Along 2, pop star Rainie Yang is box office queen of Taiwan’s horror cinema – despite not even liking the genre

Then there was the high altitude – with the team going as high as 3,400 metres above sea level. “You faint sometimes because there is a lack of oxygen and sometimes you feel dizzy and you just faint. Idris fainted for three or four minutes,” says the director.

Winslet adds: “You can’t underestimate how much energy you use when you’re working at that height. Moving at any physical pace burns your chest because it’s just harder to breathe.”

Such were the temperatures, the experience impacted upon the story. Abu-Assad recalls being so cold, when he took a hot shower in his hotel room, it brought him to tears. “The idea that you can take a warm shower … it was such luxury,” he says. “Spontaneously, I started to cry.”

The moment later worked its way into the script, as did an ad lib from Winslet about how the body adjusts to the cold. “This couldn’t have happened at the beginning of the movie,” the director notes.

The actress even endured a sequence where her character Alex, a war photographer, falls through the ice into water. Winslet drew on her water-borne Titanic experiences, in terms of telling the production how she needed to protect herself against getting hypothermia.

“I wouldn’t let the stunt double do that, I really wanted to do it,” she says. “I just really believe when you sign up to play the part, you’ve got to play the whole part. Call me old-fashioned but that’s my thing.”

Trump’s pernicious influence hung over Venice film festival, the most political in decades; John Woo thriller was a change of pace

What is intriguing is what drew Winslet to the role in the first place. Back in August 2011, she was staying on Necker Island, a private resort in the Caribbean belonging to Virgin Group founder Richard Branson, where she first met her husband (Branson’s nephew). The very next day, the house they were in burned down.

“We were all four minutes away from death and it was a completely terrifying experience. And my life changed; literally changed overnight,” she recalls.

So when she read the script for The Mountain Between Us, she related entirely to the way Alex is drawn towards Elba’s surgeon character Ben during their traumatic time together.

“We go through life and things happen; whether it’s a job that we do, someone that we meet, a country that we spend time in, [it] can have a really impactful effect on your outlook, who you are, how you think. And it was quite an important part of the story for me, the fact that I felt that so strongly.”

Did the filming change her? “For me, any acting, any film experience, any role that I play, always shifts … you shift a little bit,” she replies. “And then you settle back into daily life and just being yourself again.

“Emotionally, it probably didn’t fundamentally change. But it definitely changed me in terms of being much hardier for sure, and being more prepared for those kinds of environments, and actually really enjoying being in them for long periods of time.”

Legend of the Demon Cat: Chen Kaige adapts to China’s changed cinematic landscape with lavish production

Winslet wasn’t the only one with a smile on her face. Abu-Assad reports that studio executives were delighted with the daily footage they were sent. “Nowadays, the dailies, they’re watching actors against green screen [to enable visual effects to be added during post-production]. And they’re bored.

“When they show the dailies, they were like, ‘Oh my God!’ They don’t see these images any more, and they were so happy. I think because they were also like us; they love cinema,” says Abu-Assad.

The Mountain Between Us opens on October 5

Want more articles like this? Follow SCMP Film on Facebook