Natural & fungi textiles for training — mycelium, merino, hemp, Tencel & bamboo activewear review

Natural textiles for working out 2026 — mycelium, merino, hemp, Tencel and bamboo, ranked by what they actually do when you sweat in them

2026's 'train in nature' wave promises mycelium leather leggings, merino base layers, hemp tanks and bamboo 'sustainable' sets. We ranked the materials by what they do under real sweat load — moisture transport, thermal regulation, skin-barrier chemistry and how long they survive the wash cycle — rather than the press-release framing that puts mycelium fashion garments next to merino running kit as if they solve the same problem

The 'natural activewear' shelf splits into two products that the marketing treats as one. The first is mycelium and fungi-derived textiles — Mylo (Bolt Threads, the material Stella McCartney sent down a runway), Ephea's lab-grown mycelium surfaces, the mycelium-lined Vivobarefoot Gobi trainer and Moea's plant-based sneakers. These are genuine materials-science achievements: a grown-not-woven fibre network that competes with bovine leather on hand and carbon. They are also, in 2026, almost entirely a fashion and footwear story, not a sweat story. A mycelium leather legging is a marketing concept ahead of a material reality — the fibre architecture that makes leather feel luxurious (dense, closed, hydrophobic) is the exact opposite of what moves sweat off skin during a workout. The second product is actual natural-fibre performance fabric — merino wool, Tencel/Lyocell, hemp, bamboo — and here the evidence is the reverse of the hype: merino and Tencel genuinely outperform polyester for the skin-barrier and thermal-regulation reasons that matter to a nervous system, while bamboo viscose is a greenwashed rayon wearing a sustainability costume. The whole shelf is worth moving toward. Most of it is worth moving toward slowly, and the mycelium-for-athletic claims are worth ignoring until the material science catches up to the press release.

What it claims

'Mycelium leather activewear' — grown-from-mushrooms performance fabric, biodegradable, carbon-negative
Merino wool base layers — 'natural performance', 'temperature-regulating', 'odor-resistant', 'breathable'
Hemp activewear — 'the most sustainable fibre', 'naturally antimicrobial', 'gets softer with washing'
Tencel/Lyocell — 'botanic performance', 'closed-loop', 'silky handfeel', 'biodegradable'
Bamboo — 'the world's most renewable fabric', 'naturally antibacterial', 'silky soft', 'eco-friendly'
'Train in nature' — natural textiles are better for your skin, your microbiome and the planet than plastic activewear

What the label is not telling you

Mycelium leather is a real material — and it is not, in 2026, an activewear material. Mylo (Bolt Threads) and Ephea's Uma are grown mycelium networks engineered to mimic the collagen-bundled architecture of bovine hide. The 2025–2026 industrial-crops and materials literature (Industrial Crops and Products 2025; Chemical Engineering Journal 2026) is explicit that the open research problem for mycelium leather is durability, water-resistance and breathability under load — the same closed, hydrophobic, dense-fibre structure that makes it a beautiful handbag lining actively resists the moisture transport a workout demands. The 'mycelium activewear' you will see marketed in 2026 is, almost without exception, a mycelium-finish trim, a blended panel, or a concept garment — not a wicking performance layer. Conflating it with merino base layers is the central sleight of hand in the category.
Vivobarefoot's mycelium Gobi and Moea's plant-based sneakers are the honest use of the material. Footwear uppers, trim, and fashion garments are where mycelium belongs today; it is competing with leather, not with Dri-FIT. The New Zealand Journal of Botany's 2026 review of mycelium wearables is candid that athletic, high-wash-cycle, high-sweat applications remain a future application class. Trust the brands that put mycelium where its fibre architecture fits.
Merino wool is the natural textile with the strongest real training evidence — and it earns it. The active merino base layers from Isobaa (160/260 gsm), Icebreaker, Woolly and the Tencel-merino blends from Tripulse move moisture by a different mechanism than synthetics: the wool fibre's hygroscopic core absorbs up to ~35% of its weight in water vapour before the surface feels wet, which means sweat leaves the skin as vapour and is held inside the fibre rather than wicked as liquid along a plastic filament. The 2025–2026 trail and ultra running reviews (Run Ultra 2026; independent Fell Tee testing) consistently report merino outperforming polyester in long-duration, variable-temperature effort precisely because the wearer does not get the post-effort cold-chill that soaked synthetic produces. Odour resistance is real and is mechanical — the keratin fibre structure is genuinely hostile to the bacteria that turn sweat volatile — not a chemical finish that washes out.
Hemp is the durable, honest fibre with one real limitation for high-output work. Hemp's tensile strength, UV resistance and antimicrobial surface are well documented, and it ages beautifully — the 'gets softer with washing' claim is true. The catch for training is stiffness and moisture transport: hemp has a higher water-retention and slower dry-time than merino or Tencel, which is why the better hemp activewear labels (estroni and similar) blend it. For yoga, mobility, low-output strength and everyday wear, a hemp-blend tank is excellent. For a long run or a high-sweat interval session, merino or Tencel is the better shelf.
Tencel/Lyocell is the underrated performance fabric of the natural shelf. Tripulse's Tencel-vs-merino comparison holds up: Lyocell (regenerated cellulose from sustainably farmed eucalyptus, closed-loop solvent recovery ~99% reused) wicks faster than cotton, dries faster than merino, has a silk-against-skin handfeel, and is the natural textile closest to synthetic in dry-time. The carbon footprint is lower than cotton and vastly lower than polyester. For hot-climate training and anyone with wool sensitivity, Tencel is the best answer on this shelf.
Bamboo 'sustainable' fabric is the greenwashing trap of the category. Almost all 'bamboo' activewear and bamboo-lined sets (the Free Fly tier and most supermarket 'eco' lines) are bamboo viscose/rayon — manufactured by dissolving bamboo cellulose in carbon disulfide and sodium hydroxide, the same chemical rayon process regulated for its worker-health and wastewater impact since the 1930s. The FTC has explicitly ruled that 'bamboo' fabric made this way must be labelled 'rayon made from bamboo', not sold as 'natural bamboo'. The bamboo plant is renewable; the fabric it becomes is a semi-synthetic. It is soft and pleasant, but the 'naturally antibacterial, planet-saving' marketing is the least defensible claim on the shelf.
The thing the whole shelf is correctly running from is real. The 2024–2026 evidence on what conventional activewear leaves on the body has hardened. Bisphenols (BPA, BPS) migrate from polyester and recycled-polyester fabric, and the migration measurably increases with sweat, heat and friction (Environmental Science and Pollution Research 2024; the Center for Environmental Health BPA-in-sportswear findings on sports bras and leggings). Polyester and polyamide shed microplastics in the wash at rates of hundreds of thousands of fibres per garment per cycle, and the 2025 microplastics-and-exercise literature (PMC12403993) is now asking whether inhaled and dermal microplastic load is a meaningful input for athletes training in synthetic kit daily. For a body that spends 6–10 hours a week wrapped in hot, damp polyester, moving the next-to-skin layer toward a natural fibre is one of the more defensible 'natural' interventions in wellness — the category just needs to be navigated material by material rather than slogan by slogan.
Polyester-recycled ('rPET') activewear is not the escape it is sold as. Recycled-polyester leggings and shirts lower the bottle-to-landfill math but carry the same BPA-migration, microfibre-shed and endocrine-disruption questions as virgin polyester — and some 2024 work finds bisphenol levels higher in recycled-polyester textiles than in conventional. 'Made from recycled plastic bottles' is an ocean-plastics story, not a skin story.

Effect on the nervous system

The nervous-system read on activewear is mostly thermal, mechanical and chemical, and the body registers all three continuously. Thermally, a fibre that holds sweat against skin — soaked polyester after a long effort — produces a rapid evaporative-cooling drop that reads as a threat signal to a warm system suddenly cooled; the active merino and Tencel literature consistently reports less of this post-effort chill because the hygroscopic core buffers the transition. Mechanically, C-tactile afferents read texture and breathability all day (McGlone 2014; Craig 2002 — the same interoceptive-skin work cited across our anchors), and a soft, breathable natural fibre removes a small but constant low-grade friction signal that a stiff, hot, damp synthetic emits during training. Chemically, the bisphenol and microfibre story is the load the body is actually metabolising in 2026: sweat, heat and friction increase dermal absorption of what the fabric is made of, and for someone training daily in the same synthetic set the chronic input is non-trivial. None of this is acute. The felt effect over a season of migrating the next-to-skin training layer to merino or Tencel — and keeping the wash away from fabric softener (see our laundry review) — is less reactive skin in the friction zones, fewer post-effort chills, and a quieter chemical baseline. That is a regulation input the marketing is pointing at for the wrong reason but pointing at the right thing.

Who it might suit

Endurance and trail runners, hikers and anyone out for hours in variable weather — merino base layers (Isobaa 160/260, Icebreaker, Woolly) are the strongest evidence-based pick on the shelf. Hot-climate and indoor training in Tencel/Lyocell (Tripulse and equivalents) for fast dry and skin comfort. Hemp-blend tanks and leggings for yoga, mobility, low-output strength and everyday wear. Anyone with reactive skin, eczema, contact dermatitis or a fragrance/chemical sensitivity that the synthetic-set-and-sweat combination provokes. Anyone curious about mycelium for footwear, accessories or a statement fashion piece — buy it there, not as 'performance kit'.

Who should skip it

Anyone buying a 'mycelium activewear' or 'mushroom performance' garment expecting wicking, durability and wash-cycle survival on par with merino — the material science is not there yet and the price is. Anyone treating bamboo viscose as a natural, antibacterial, planet-positive fibre — it is soft rayon with a greenwashed label; if you love the handfeel, enjoy it, but discount the claim. Anyone assuming 'recycled polyester' solved the skin and endocrine questions — it shifted the ocean-plastic story and left the BPA and microfibre questions intact. Anyone replacing a whole synthetic wardrobe in a single expensive drop — migrate the next-to-skin, high-sweat, high-contact layers first (sports bras, base shirts, underwear, socks) and keep outer layers until the budget catches up.

Bottom line

Honest hierarchy for the natural training shelf: (1) Merino wool base layers (Isobaa, Icebreaker, Woolly) for endurance, trail and variable-weather work — the strongest evidence, best thermal regulation, real odour resistance. (2) Tencel/Lyocell (Tripulse and equivalents) for hot-climate, indoor and fast-dry needs, and for anyone wool-sensitive. (3) Hemp-blend for low-output, yoga, mobility and everyday — durable and honest, just not the high-sweat pick. (4) Mycelium leather in footwear, trim and fashion (Vivobarefoot Gobi, Moea, the Stella McCartney Mylo pieces) — a real material, used where its fibre architecture fits; ignore 'mycelium activewear' performance claims in 2026. (5) Bamboo viscose if you enjoy the softness, labelled as rayon and with the green claims discounted. (6) Recycled polyester if the ocean-plastics argument is your priority over the skin-and-endocrine one. (7) Virgin polyester/spandex — keep it for outer layers and low-contact gear, move it off the high-sweat next-to-skin surface over time. Pair any of this with the detergent reform in our laundry review — a natural fibre laundered in fragranced quat-loaded softener gives back half the gain. Track skin, thermal comfort and sleep through the swap in a Kokorology Journal; the Skin & Beauty Anchor covers the interoceptive-skin frame and the Cortisol Anchor covers the post-effort thermal load the fabric is buffering.