While the UK is being roasted by Europe's blistering 'heat dome' – with temperatures reaching 36.1C yesterday – it's not suffering quite as much as our neighbours in France.There, in some parts, the mercury hit 44C (111F), the hottest since records began.So stifling was it in Paris that the Eiffel Tower was closed, alongside several museums and as many as 1,800 schools.All of which is making the City of Light's menswear shows less pleasant than usual.But it's not a lack of air-conditioning or bottled water that's galling – it's the fact that many guests are opting for clothes more suited to a cold snap.Nowhere was this more apparent than at Tuesday night's Yves Saint Laurent show, where the fashion stars were shining. Or rather, perspiring.Kate Moss, 52, queen of 'boho chic', could have sported the look she made famous in the early 2000s, but instead wore heavy dark grey jeans, her only concession to the heat being they were rolled up at the ankle.And while her black lace camisole top was summery, her black jacket signalled a different season entirely. Kate Moss attends Saint Laurent during Day One of Paris Fashion Week - Menswear Spring/Summer 2027 on June 23 Sienna Miller upped the winter ante in a beige slip dress with a fur-trimmed coat at the Serpentine Gallery Summer Party on 23 June Pictured: Connor Storrie at the Saint Laurent Menswear Spring/Summer 2027 show as part of Paris Fashion WeekWas it leather, or a marginally less sweaty duchess satin? Either way, she kept it on for the whole show. But she looked positively beach-bound compared to outfits worn by her neighbours on Saint Laurent's front row. To her left was actor Rami Malek, 45, in black pinstripe trousers, striped shirt and navypolka-dot tie, topped off with a black leather blouson jacket.To her right was another actor, Connor Storrie, 26, right, who wore a belted black plastic mac that would have been handy in a shower, but not a heatwave. While he removed it before taking his pew, he kept his shiny black PVC knee boots on. The star of Heated Rivalry probably had overheated feet.Even singer Charli xcx, 33, who at first glance looked weather-appropriate in a lacy red slip dress, turned out to be wearing leather.And while Madonna, 67, may have looked like she was wearing her long-sleeved, high-necked lace mini dress with bare legs, in fact, she had teamed it with tights. Fishnets, but still tights. Proof she's still a material girl, even in high summer. Given these A-listers have their pick of the world's coolest clothes in both senses of the word, it might seem strange that they reach for leather rather than linen.But when you are a guest at a designer's show, you're duty-bound to dress in a way that promotes them. So if that designer is pushing leather and PVC for winter, that's what it's incumbent on you to wear. Yes, even in a heatwave. While the high street has a shorter production cycle, the luxury end of the fashion industry typically works six months ahead.In June, guests at Paris menswear week showcase designers' autumn/winter 2026 collections, wearing the forthcoming pieces on the front row.In doing so, they drive customer awareness, which designers hope will in turn boost demand. It's like being a walking billboard, only far more handsomely paid.It wasn't just in Paris that the A-list was set on looking hot. At the Serpentine Summer Party in London on Tuesday, actress Sienna Miller, 44, upped the winter ante in a beige slip dress with a fur-trimmed coat.The embroidered satin coat, by British designer Conner Ives, features thick fur-trimmed cuffs and a wide fur trim described online as '100 per cent vintage blue fox'.The coat is sold out, but it's thought to have retailed for £6,480. Some may say that's a high price to pay for looking trendy – particularly in 30C heat.While Ms Miller, who gave birth to her third child six weeks ago, looked radiant, even her most ardent fans are unlikely to be persuaded to wear fur in a heatwave.She might have inspired us to wear coin belts, cowboy boots and the entirety of her recent M&S collection, but this is one trend the rest of us will be sitting out – in cotton.