Jake Gyllenhaal is known as an actor who goes through incredible physical transformations in order to get into his onscreen roles. For Southpaw last year, he famously trained with boxing pro Terry Clayborn for eight months, doing up to 2,000 crunches a day and packing on 15 pounds of rippled muscles to become Billy “The Great” Hope. Before portraying a nocturnal paparazzo in Nightcrawler, Gyllenhaal lost close to 30 pounds by eating mostly kale salads and religiously running 15 miles a day. But for his new film, Demolition, opening in theaters Friday, April 8, the biggest physical transformation he went through was letting his body hair grow out.

As the 35-year-old actor told the crowd after the film’s premiere at SXSW, “I was actually a little embarrassed to play the part because sometimes I felt like the character was really close to myself, but that’s all that [director] Jean-Marc [Vallée] wanted,” Gyllenhaal said. “I’m thankful to him for that.”

That is not to say his Demolition character doesn’t undergo a tremendous metamorphosis, but the changes are of an internal nature. Jake plays Davis Mitchell, a successful Wall Street banker who seems to have a picture-perfect life until his beautiful wife dies in a car accident. Davis wanders through the next inevitable phases of his life in a fog, struggling to understand his feelings, express his grief properly, and find joy again. His solace comes from an unlikely hobby he discovers after an encounter with a faulty vending machine: taking things apart. It also puts him in touch with customer service rep Karen Moreno (played by Naomi Watts) and her rebellious tween son, Chris (Judah Lewis). The three form an unlikely bond, and Davis’s manic deconstructions ultimately help him put himself back together again. Surprisingly humorous and extremely heartwarming, early reviews are saying this is Gyllenhaal’s best performance since Brokeback Mountain.

InStyle spoke to Gyllenhaal by phone to discuss his role and the making of Demolition, including how clothes helped him get under his character’s skin and what it is really like to free dance down a busy Manhattan street. Despite hopping on the call an hour and a half after the scheduled time, Gyllenhaal bubbled with charm and enthusiasm, clearly an artist proud of his latest work.

Jake Gyllenhaal: Sorry I am late. I was just getting dressed for this interview.

InStyle: I hope you’re wearing a Tom Ford suit, like you did to the premiere in Austin at the SXSW Film Festival a few weeks ago.

JG: Well, that’s what I wear, always. No matter what I am doing. It doesn’t matter. You can’t do anything, unless you’re in a Tom Ford suit.

At that screening, you stayed in the theater and watched the whole film. Was there anything about the final cut that surprised you?

No, when you are in the process of making a movie the final cut is a real statement of vision and point of view of the director. All the way up to that moment, every bit of tweaking can really change a movie, particularly if you know it so well that the details are really important to you. I just think I realized a number of things about the movement at the end of the movie and a realization about what this character goes through. I always knew they were there but I wasn’t sure if they were fully communicated. Also, to see it with an audience was just lovely. They knew that it was meant to laughed be at and laughed along with it in all the right spots.

That is one of the surprising things about the film. It sounds as though it would be so depressing, but it is actually packed with LOL moments.

The triumph of the human spirit is really prevalent in all of Jean-Marc’s movies [like Wild and Dallas Buyers Club] that sort of love of being human.

Your character’s transition is partly demonstrated through the clothes he wears. For example, there is a scene when you put on Carhartt work pants that don’t really fit, and you wear them with suspenders and a work dress shirt. It’s an odd look.

That idea came to me during a break between doing Southpaw and Demolition. In that time, I try to open my eyes to the world to see if there is something that will inspire me. I was walking down the street and I saw this construction worker—and he was wearing these oversize Carhartts with suspenders with this cut-off shirt and work boots and I thought, “Oh sh—, that’s Davis.” In the script [by Bryan Sipe] there were so many references to both my character and Chris Cooper’s character [who plays my father-in-law] wearing suspenders that I thought, “Oh wow, what a cool transition if he uses his suspenders.” Something just clicked.

The scene where he gets them and puts them on is funny, because anybody who has ever touched them knows that they are the stiffest, most uncomfortable thing straight out of the box.

I personally am not a big fan of trying on things. I have like one pair of pants and that is sort of what I always wear. I imagined the character running through store and going, “This looks like it will fit,” without trying it on, and then discovering that they are way too big—but then going, “Ah, f— it. It’s OK. I’ll just put it on, it’s fine.” That then becomes his style.

In addition to your costumes, the other transformation you go through in Demolition is a grooming one. You get progressively hairy as the film goes on!

That was the director’s idea. He had spent time with this guy in the financial world for the movie, and saw that he plucked his eyebrows and did all this [manscaping] stuff. He wrote a sequence into the movie after seeing how groomed that whole world can be and he just really liked a guy who kept up with this conventional idea of what he needed to do to be accepted early on but then kind lets it go as the movie goes on.

Was there a body hair continuity expert on set?

No, but it sounds like that is probably your area of expertise [laughs].

Tell me about the scene when you are listening to music on headphones, and dancing through the crowded N.Y.C. streets.

I believe in making moves as a way of actually engaging and connecting in the world as opposed to just commenting on it, apart from it. It is great fun whenever you can to be in a scenario that is real, when you don’t have actors portraying people who are extras. [For those scenes] we spent half a day shooting through Lower Manhattan and I danced through real construction sites and commuters and on trains. Obviously the idea of dancing openly in a public space is embarrassing for people who can’t dance like me, but at the same time, it also embodies the essence of the movie. In the end, even though I was nervous about doing it early on, it became so fun.

What music were you listening to as you danced?

I honestly don’t know. Jean-Marc gave this iPod with all these shuffled songs that he put on there and I didn’t know any of them. I mean maybe he thought I would know them but I really did not know them. I could not tell you what they were. I just danced to random songs.

You do a lot of actual demolition work in the film. Had you ever wielded a sledgehammer before that?

My dad was a really good carpenter and I painted houses throughout college, so we built a lot of things around the house when I was a kid. But I never did anything like that in a professional sense. I demolished my kitchen in my old house with my friends and I have done some of that work for friends who are doing their own houses.

That sort of work can be very therapeutic.

Anything can be therapeutic if you really need to do it and you believe in it but, yes, it’s cathartic in a way—it’s an expression. What I learned in this movie is that apathy has a quality to empathy. We really don’t give it the service that it’s due. It’s OK to walk around not knowing what you feel. I think we put a lot pressure on ourselves to feel a certain way and society certainly tells how we are supposed to look and how we are supposed to feel sometimes, and we don’t know how we are supposed to feel. And that’s OK too.

Catch Demolition in theaters from Friday, April 8.