Do you need to detox your sportswear?

It’s a wet, windy morning on Parliament Hill in London. The steep, eight-minute incline means you are cold, reluctant and full of dread at the bottom and hot, sweaty and triumphant at the top.

The kit I usually rely on to regulate temperature and fend off the elements is a triple-decker sandwich of petrochemical-derived synthetics. Not today. I am wearing castor bean oil-based leggings (from Pangaia), a wool sports bra (Branwyn), a merino-wool base layer (Icebreaker) and an alpaca-lined rain-resistant jacket (Mover). On my feet are a pair of Allbirds runners made from the natural fibre biomaterial Mirum. This is the new wave of performancewear – and it has kept me cool, dry and odour-free the whole way up.

Before synthetic materials, there were natural ones. In 1954, Roger Bannister ran the four-minute mile in cotton shorts and top. In 1979, Sir Ranulph Fiennes crossed the Arctic wearing a 100 per cent Ventile cotton suit. The same material was worn in 1953 by Edmund Hillary and Tenzing Norgay to summit Everest.

From the ’80s onwards, synthetic fabrics dominated the market: Jane Fonda’s shiny aerobic leotard, Champion’s compression sports bra, Lululemon’s yoga pant. Alongside Lycra and Spandex came Gore-Tex, bringing unrivalled protection against the elements.

But the cost of petrochemical-derived synthetics is now being counted. Microplastic shedding, created from friction and washing, pollutes oceans and has been found in drinking water. PFCs (perfluorinated chemicals) – also known as PFAs (per- and polyfluoroalkyl substances) and “forever chemicals” – are added to enhance moisture wicking, water and flame-resistance and the adherence of colourful dyes. Some variations have already been globally banned owing to their links to liver damage, cancer and reproductive problems; however, the use of other PFAs in clothing is still common, and is mostly invisible and undeclared.

Finisterre Stormbird waterproof jacket, £250

The dye industry is another toxic mess. To give an idea of how strong some dyes are, the harshness can turn 100 per cent cotton fibre into a comparable microplastic. “There’s not much cotton you can buy that is all-natural – it has all been treated and dyed,” says A Todd, head of design at Finisterre, a fluorocarbon-free outdoorwear brand. “There are more cotton fibres in the ocean than any other textile fibre, and many can’t break down because of the dye treatment on them.”

What’s more, “polyester doesn’t take on chemicals and dyes as readily as natural fibres”, reports George Harding-Rolls of Eco-Age. “So you need to use more chemicals to achieve the same effect.” The potential side effects of these are exacerbated when used in activewear because the clothes sit against the skin, increasing the potential to be absorbed by the body.

“People think it’s the fibre doing the job, but often it’s the chemical finish the fibre has been treated with,” says green chemistry pioneer Matthias Foessel of Beyond Surface Technologies. To replace petroleum-derived chemicals, Foessel looked for similar molecular structures in nature, eventually alighting on micro-algae oils, plant seed oils and a plant wax. “The algae we use for wicking comes from a walnut tree, and the natural wax water repellent from the candelilla plant.” His products have been used by Adidas for its football shirts since the 2014 World Cup, and also by Lululemon, Patagonia, Puma and others.

Community Clothing cotton Breathable T-shirt Plastic Free, £35

Community Clothing plastic-free cotton T-shirt, £35

Community Clothing cotton Lightweight Running Short Plastic Free, £49

Community Clothing plastic-free cotton Lightweight running shorts, £49

Those brands making the move away from synthetics consider toxic chemistry a fundamental issue. “We have not included any synthetic finishing on our fabrics: no waterproof coatings or non-iron treatments,” says Patrick Grant of Community Clothing, whose collection of 100 per cent natural fibre activewear is at the vanguard of a return to naturals. “All performance is achieved through the mechanics of the way we weave and knit.”

Swiss sportwear company Mover is perhaps the most technologically advanced natural activewear brand. In October last year the brand announced that its water-resistant jackets, thermo-insulating base layers and wool fleeces are now 100 per cent plastic free. “We were not happy with synthetic performance,” says CEO Nicolas Rochat. “We missed breathability: polyester is light and efficient in terms of warmth, but it gives heat back to the body much too quickly. You sweat more. Every mountaineer will tell you that the biggest enemy of cold on a mountain is warmth, because when you are too warm you start sweating and condensing. So when it gets cold you are freezing. Every time we climbed a corridor up a mountain, we had to take the Gore-Tex shell off, put it in our backpack, and then put it on again when we got to the peak.”

Mover cotton and Swisswool Light Jacket, around £375

Mover cotton and Swisswool light jacket, around £375

Mover wool-jersey merino T-shirt, around £85

Mover wool-jersey merino T-shirt, around £85

Mover retained a wool lining and switched out the Gore-Tex for Ventile, the cotton fabric developed for pilots in the second world war. “We tested it for skiing, and for the first time we felt we really could breathe, from the skin to the outer shell. It was resistant to the wind, snow and light rain.” Meanwhile, the natural fibre’s odour-control, anti-static, thermoregulation and comfort was superior to synthetics. “Why have we worn these scuba diving outfits for the last 40 years instead of something more comfortable like our parents and grandparents?”

Icebreaker merino-mix Realfleece Descender hoodie, £175

Icebreaker is also on the plastic-free journey – not quite at 100 per cent, but nearly. This winter, creative director Neil Baker jumped in a lake wearing one of the brand’s merino and Tencel base layers, with a friend wearing one in polyester. “The lake was 50 degrees Fahrenheit. His T-shirt when he got out was reading 47 degrees; mine read 73.” Its water-repellent wool jackets “won’t perform at the same level as Gore-Tex but are fit for purpose in certain environments and activities. Ask yourself, ‘Am I climbing Everest or going for a weekend in Chamonix?’”

Branwyn Essential bralettes, $48 each, and Essential bikini, bottoms, $36

These new technical woollen yarns have also found their way into underwear. Branwyn’s wool-mix bra has enough support for low-impact activities such as yoga and hiking, but the warmth and breathability it provides conjures a whole new feeling to those who have only ever worn nylon sports bras. “Ours are Oeko-Tex certified and toxic chemical free, although we have retained a small percentage of elastane and nylon for integrity: we are 81 per cent wool, core spun so the nylon fibre doesn’t touch the body,” says Branwyn president (and climber) Deanne Buck. As for the bottoms, the wool content allows for change in temperature, wicking and evaporating. “It’s good for skiing when you are going hard and then stop. We don’t talk about the role bottoms play in gynaecological health, but we should.” Mate The Label does similar with cotton: its sports bras and leggings are made of 92 per cent cotton, eight per cent Spandex and a promise of “no pesticides, microplastics, formaldehyde, carcinogens or endocrine disrupters”.

Prada Linea Rossa x Woolmark wool cardigan, £2,000, and matching leggings, £1,600

Over at Prada Linea Rossa there is a collaboration with The Woolmark Company for natural garments: four pieces in the collection are crafted with 100 per cent wool, including a zipped sweater, trousers, a neck warmer and beanie. Prada has employed innovative dyeing and finishing treatments on this technical line, along with chlorine-free colours and finishes.

However, there is simply not enough cotton and wool in the world to clothe the human race. Pangaia hopes that plant-derived biomaterials will replace petro synthetics, as in its EVO, a nylon sourced from castor beans, with an equally innovative part-bio-based elastane for stretch. The material is slightly thicker than you would expect, but achieves excellent breathability; however, the castor beans are put through a polymerisation process which impacts biodegradability.

Allbirds Mirum Plant Racer trainers, £120

Natural Fiber Welding’s Mirum is perhaps the most promising biomaterial to date, due to its biodegradable qualities and durability. Says founder Dr Luke Haverhals, “If you can start with things that are part of nature’s natural circle, if you don’t make them toxic while you’re manufacturing them, then they can end back with nature.” Mirum achieves many of the same performance markers as leather and is almost indistinguishable. Also in the Mirum family are Clarus, Tunera and Pliant: biotechnologies that allow for moisture-wicking and water-resistance.

For now though, responsible performancewear brands looking to produce at scale are taking the recycled polyester route. It’s the one chosen by Stella McCartney for Adidas, and brands such as Finisterre – which uses ECONYL – and Patagonia – which uses NetPlus, a material made from recycled fishing nets, the use of which funds ocean clean-up. While Patagonia promises to phase out PFCs by 2025, Finisterre has already done so, and also recommends doing it yourself. Greenland Wax, which comes in bars, can be rubbed over your jacket and then dried off with a hairdryer. “You can get an incredible amount of water repellency from that,” adds Todd.

I’m not sure I’ll need it. After several days in my all-natural running kit, none of my garments needed washing. Hung out to dry on a hanger, the wool fabrics do exactly what they would on a sheep: keep me warm, cool, dry and comfortable. Hills notwithstanding.