“I’m very phobic about plastic,” says Ms Gabriela Hearst. The Uruguayan fashion designer might be in the business of making classic, beautifully tailored clothes, but she is doing her level best to do it in a modern way: ethically and sustainably. In fact, she is one of the industry’s most prominent voices on sustainability. “Everything we do, from the resourcing of the materials to the manufacturing, we make sure they’re less wasteful, we make it as sustainable as possible,” she says.

Fortunately, clothes from Gabriela Hearst are not the kind of thing a person might wear once before they’re tossed to the back of the wardrobe. Invariably crafted from brilliantly luxe materials and with a fastidious attention to detail, there are few garments that exist in the world that have as much care, attention and quality poured into them. Having built up this reputation with tailored womenswear, Ms Hearst has now branched out into menswear.

It isn’t a straightforward thing to for a womenswear brand to leap across the gender divide, but Ms Hearst is well-poised for it. Minimalist suiting in rich materials and sophisticated colours are the designer’s bread and butter. “The array for men’s materials is much wider in fine wool suiting, so I’ve always used men’s fabrics anyway. Our collections have always had a masculine edge,” she says.

Still, Ms Hearst is clever enough to know that to make great menswear, she needed another perspective. “I understand women’s psychology, but I needed a guy who understands men’s psychology, because we’re kind of a different species,” she jokes. She uses her husband – the media scion and philanthropist Mr Austin Hearst – as a sounding board for her designs, but it was Mr Peter Miles, the brand’s art director (and the man responsible for designing some of the most prominent logos and advertising campaigns in the fashion industry, for brands including Marc Jacobs and Celine), with whom she chose to develop her menswear collection. “There are very few people that I trust in the level that I trust Peter,” she says.

“Miles grew up in London during a really interesting period of time, during the 1980s and 1990s. He brings an edge of cool to the clothing, but mixes that edge with a precision. He can be very meticulous [about the space] between two letters, and that’s something he’s put into the collection as well,” she explains.

What Ms Hearst brings is a more rustic, approach informed by her upbringing (she grew up on her family’s ranch in central Uruguay), and the comforts of country living. “So, the fluffy cashmere and the sweaters with the little mélange on, Peter would be like, ‘why are you doing a sweater with bits on it?’ and I’m like, ‘Because this is what men in the country want to wear. Plus, it’s nice!’” Together, the designer and the art director worked for over a year and a half to refine what exactly the Gabriela Hearst menswear collection would look like. “We analysed what the essential parts of the wardrobe would be that we would start building, and we took a long time to do this, tweaking it until it was ready.”

Now that it is ready, who is the man she intends to dress? As it happens, Ms Hearst’s manifesto for her menswear came in the form of an article written by journalist and her late mother-in-law, Ms Austine McDonnell Hearst, circa 1950 on what might constitute the “Ideal Male Fashion Plate”. It advises that “Men should aim for nonchalance, individuality, without novelty,” and warns against men wearing short shorts: “Women do not feel about an expanse of hairy leg the way men feel about TV necklines.”

Happily, this fitted with Ms Hearst and Mr Miles’ idea for their menswear so succinctly that they have republished it as the press release for the collection. “The man we’re dressing hasn’t really changed since she wrote that,” Ms Hearst explains. “He’s an open man who is elegant, but not fussy, who doesn’t pay too much attention to what he wears. He definitely doesn’t wear diamonds; diamonds are not his best friend.”

The effort Ms Hearst puts into creating timeless clothing means that, although she pays meticulous attention to detail in the cuts and fabrics of her clothing, she doesn’t follow trends. “Yeah, there was something, I think, called streetwear going on while we were doing our collection?” she jokes. “Seriously though, if I see another ugly sneaker, I’m going to die!” Instead, Ms Hearst’s menswear collection is filled with clothes that are intended to be worn for decades. There’s a lavender-checked, double-breasted suit that looks equally elegant with sneakers or smart shoes, a cashmere and silk reversible hoodie, and a trench coat that Ms Hearst calls “insane” because it is so beautifully crafted and has an interior strap you can attach to your leg while riding a bicycle.

Regardless of whether she’s designing for men or women, Ms Hearst’s main focus remains sustainability and action. “The time for good intentions regarding the environment is over,” she says. The designer is currently working on moving her supply chain as far away from virgin materials as possible. All of the brand’s packaging is now biodegradable; product is shipped with a cardboard hanger and compostable TIPA plastic that biodegrades in 180 days as opposed to 25 years. Plus, if there is excess fabric from the men’s collections, for instance, it is used to make the women’s, and vice versa.

“The less we take out of this planet’s resources right now, the better. A lot of people say ‘save the planet’, but the planet is going to be around, it’s just going to be around without us,” she says. A depressing thought, but if more fashion designers were as diligent as Ms Hearst is in her approach to clothes, we might have some hope. “I know every garment, and I know how they are brought into this world. And if they’re going to take up space in this world, they better be good.”