Gabriela Hearst, a favourite fashion designer of Oprah Winfrey and the Duchess of Sussex, describes her business model as “cooking with leftovers”.

Cashmere leftovers, that is. With her husband, John Augustine Hearst, scion of the magazine empire, the fashion designer has a net worth estimated at £1.5bn, and has made it her mission to develop a sustainable methodology for the fashion industry.

The theme of Hearst’s latest catwalk collection was “waste”, she said backstage before her New York fashion week show. “Maybe it doesn’t sound so glamorous,” she shrugged, “but it’s what we should all care about, no?”

A model at Gabriela Hearst’s show. Photograph: Pixelformula/SIPA/Rex/Shutterstock

Hearst has a very considerable business advantage. Her chic, upscale label has become a status symbol within a numerically tiny but economically powerful fashion constituency who wish to dress to signal that they have meaningful values, as well as excellent taste. As a result, she encounters no price resistance to upcycled cashmere coats with four-figure price tags.

This season, instead of sketching designs and then placing a fabric order to fit, Hearst bought up small runs of quality fabric sitting unused in warehouses. “There is so much beautiful fabric already out there. So I bought this wonderful black cashmere and designed into it, rather than the other way around.” On the catwalk, coats and blazers were constructed from strips of cashmere fused together with slender black leather stitches.

Unsold pieces from previous seasons were also given a second life. “How do you repurpose your stock, and make it fresh again? If it’s beautiful material, it must be possible, right?” Hearst reasoned. Two coats in a classic princess-line silhouette – one camel, one navy – were cut into sections and reconstructed, so that a camel coat now has a navy lapel and a navy band at the hem, and vice versa.

Hearst – “a huge, huge Dylan fan” – had a series of 1960s portraits of Bob Dylan wearing a patchworked, multicoloured jacket pinned to her backstage mood board, which she called “the aesthetic, the subconscious” of her collection. The photos were the inspiration for coats constructed out of Turkish rugs which “were being thrown away by the market, because they were damaged or had holes”. (A cashmere lining solved the scratchiness issue.) Safari-style suits with softly flared trousers came in 1970s shades of olive, toffee and mustard.

Hearst begins making handbags only after clients have placed a deposit, to avoid overproduction. (Despite the £2,000 price tag, some of the bags have a longer waiting list than an Hermes Birkin.) But the goal of carbon neutrality is still a work in progress, with her biggest challenge the carbon footprint of transporting product. She has switched from air freight to shipping where possible, but “we still need to work on timing to improve efficiency, so there are fewer journeys”, she said.

Hearst, who is a board member of Save the Children, has been providing financial backing for a group lawsuit of young people suing the US government for failing to protect their future human rights by ignoring the climate emergency.

Gabriela Hearst on the runway. Photograph: Pixelformula/SIPA/Rex/Shutterstock

Last year, she opened a flagship boutique in London designed by Norman Foster. Upcycled wood from a military barracks in Shropshire have been transformed into parquet flooring, while the display cases are carved from trees felled during a storm.

“It’s important that we do what we can to feel good about what we do, to make it joyful,” said Hearst. To spread that joy, scraps of cashmere left over from past collections were made into sleep masks, which were gifted to show attendees.