Four years ago, one man’s cosy puffer jacket sent a tremor through the fashion industry. It was January 2019 and fashion’s glitterati had congregated in Paris’s Tuileries Gardens for the Louis Vuitton fashion show – a sea of elegant earth tones and sumptuous natural fabrics. But then came American rapper Frank Ocean, wearing tattered jeans, hiking boots, a woolly hat and an orange down jacket by the very un-chic adventure-wear brand, Mammut. It was a style better suited to the Lake District than Paris Fashion Week, but one that’s a near-universal look now. At its height, this trend was known as “Gorpcore” – a reference to an American hiking snack – and basically meant wearing extremely expensive clothing designed to keep you alive in the harshest possible conditions. “There’s an appetite in the fashion and lifestyle market to buy into that super technical look,” says Fiona Taylor, head of design at British outdoor brand Berghaus. “They’re not going up a mountain; they’re going down the pub on a Friday night. But it’s a jacket that …