COMPARISONS
What merino actually does on the body
Merino wool comes from a specific breed of sheep whose fibre is much finer than commodity wool. Good-quality activewear merino is under 18.5 microns in diameter, often under 16. Below 22 microns, wool stops feeling scratchy to most wearers. Below 18.5, it feels soft against skin.
Three properties make merino unusually well-suited to active wear:
Thermoregulation. Merino's fibre structure traps small air pockets that adjust to ambient temperature. The same garment keeps you warmer in cool weather and cooler in warm weather than a synthetic of equivalent weight. This is why merino base layers dominate outdoor sportswear.
Moisture wicking. Merino moves sweat from skin into and through the fibre, then releases it through evaporation. The skin contact stays drier under sustained sweat than cotton.
Natural odour resistance. This is where merino is genuinely ahead of cotton, and it is worth being precise about why, because the marketing usually gets it wrong. Wool is keratin, a protein whose structure absorbs moisture vapour deep into the fibre rather than leaving it on the surface. Odour bacteria feed on the compounds in sweat sitting on the skin and fabric surface, so a fibre that pulls that moisture inward gives them less to work with, and the scaled cuticle is a poor surface for them to colonise. Lanolin is often credited as a "natural antimicrobial," but most of the lanolin is washed out during scouring before the wool is ever spun, so the moisture behaviour, not a residual grease, does the real work. The practically important part: merino stays fresh without any added antimicrobial finish, and those finishes are a common skin-reaction source in synthetic activewear. A merino base layer can typically be worn three or four times without smelling, which makes it the strongest choice for multi-day travel.
How merino is actually made, and where it stops being clean
The fibre's headline advantage is that it needs very little processing to perform. Sheep are shorn, and the raw fleece is scoured: washed in warm water with detergent and mild alkali to strip grease, dirt and most of the lanolin. From there it is carded and spun into yarn. Compared with the solvent chemistry behind regenerated fibres, or the bleach-and-formaldehyde finishing common on conventional cotton, that is a short and comparatively low-chemical route. On raw-fibre processing, merino is one of the cleaner options available.
The honest caveat is the finish. Untreated wool felts and shrinks when it is machine-washed and tumbled, which is a real problem for daily activewear. The standard fix is the "superwash" treatment, and it is the least clean step in merino's chain. It works in two stages: chlorine (as hypochlorite or chlorine gas) partially etches away the fibre's cuticle scales, then a thin cationic polyamide resin, usually Hercosett, is coated over the fibre to seal it and stop the scales from locking together. Both stages generate wastewater carrying AOX (adsorbable organic halides), a persistent chlorinated pollutant that regulators in developed markets cap and that responsible mills now capture and neutralise rather than discharge. Newer chlorine-free routes exist (enzyme, ozone or salt-based oxidation) but they are still the minority.
So "merino is a clean natural fibre" is true of the raw wool and misleading about a typical machine-washable merino legging. If processing chemistry is the reason you are choosing merino, look for non-superwash or explicitly chlorine-free machine-washable merino, and accept that non-superwash wool demands gentler washing in return.
Where merino wins for gym training
Cardio sessions, especially indoor cycling, spin, HIIT. Heavy sweat, high heat, and the need to manage moisture without changing clothes between exercises. Merino performs well across all three.
Hot yoga and heated studio training. The thermoregulating effect helps, and merino moves moisture better than cotton in sustained-sweat conditions.
Travel training. When laundry is intermittent, the ability to wear merino multiple times without odour is a meaningful advantage. Hotel gym training during business travel is a strong merino use case.
Outdoor cardio in mixed conditions. Running, hiking, trail work in changeable weather. Merino's temperature regulation outperforms most natural fibres here.
Where merino loses to cotton
Strength training with high friction. Squats, deadlifts, lunges, mat work. Merino pills under repeated friction, especially at waistbands, seat seams, and shoulder straps. Cotton holds up better through hundreds of training sessions.
Daily training durability. Merino activewear typically needs to be replaced sooner than cotton activewear if it sees five or more sessions per week. The fibre weakens through repeated stretch and friction more than cotton does.
Care complexity. Most merino activewear cannot be machine-dried, has specific wash temperature requirements, and benefits from mesh laundry bags to limit snagging. Cotton activewear handles standard washing and drying without ceremony.
Cost. Merino activewear typically costs three to four times what comparable-quality cotton costs. At the scale of building a full activewear wardrobe, the difference matters.
Vegan concerns. Merino is an animal-derived fibre. For wearers who avoid animal products, merino is not an option regardless of performance.
The micron question
The "merino itches" reputation is real for coarse wool. Modern activewear merino is fine enough that this concern is mostly historical. Quality activewear brands disclose the micron count (look for under 18, ideally under 17). Cheap merino blends sometimes mix in coarser wool to lower cost, which brings back the scratchy feel.
If you have tried merino activewear and found it itchy, the micron count was probably high. Trying a different brand with a documented fine-micron count usually resolves the issue.
What "merino blend" really means
Most merino activewear at affordable price points is a blend with synthetic fibres, often polyester or nylon, plus a small percentage of elastane for stretch. The synthetic percentage matters: a 65% merino, 30% polyester, 5% elastane blend is doing more polyester duty than the merino marketing suggests.
For the merino advantages (odour resistance, thermoregulation, sensitive-skin compatibility) to fully apply, the merino percentage needs to be high enough to dominate the fabric. Look for 80% or higher merino in the blend if those properties are why you are choosing it.
Where LAINE HILL sits
We tested merino blends during the early LAINE HILL prototyping phase, carefully weighing the advantages and trade-offs. At the start of the brand we also wanted to keep LAINE HILL more accessible, which led us to choose organic cotton for our first collection. The advantages of merino are real but the trade-offs (durability through wash, pilling at high-friction points, care complexity, cost) did not match the training pattern most LAINE HILL wearers do: indoor sessions, mixed studio and gym, walking, low-to-mid impact, year-round.
For outdoor cardio in changeable weather and for multi-day travel where odour control matters, merino remains a legitimate alternative to LAINE HILL cotton. We are not competing for those use cases. We are competing for the daily indoor-training pattern that cotton outperforms merino on cost, softness, durability, and washability.
If your training mix is heavy on cardio and travel, merino is a strong choice. If your training mix is daily indoor or mixed studio work, the LAINE HILL set holds up better through the wash cycle and costs a fraction of what merino does, with the same clean-chemistry skin profile.
Common questions
Is merino wool good for the gym?
For cardio, hot yoga, and high-sweat training, merino performs well thanks to thermoregulation and fast moisture wicking. For strength training and pilates with repeated squats, lunges, and floor work, merino pills faster than cotton at the high-friction points. The best fit is mixed training with frequent travel, where odour resistance matters most.
Does merino wool actually not smell?
It resists odour better than any other common natural fibre, and the reason is mostly physical, not antimicrobial. Wool is keratin, a protein that absorbs moisture vapour deep into the fibre, so sweat is held away from the surface where odour bacteria feed, and the scaled cuticle gives bacteria little to colonise. Lanolin is often credited, but most of it is scoured out before the wool is spun, so the moisture behaviour does the real work. The upshot that matters: merino needs no added antimicrobial finish to stay fresh, which removes one of the more common skin-reaction triggers in activewear. A merino top can typically be worn three or four times before it starts to smell.
Is merino itchy against the skin?
Coarse wool (over 22 microns) is itchy. Modern merino activewear uses fine-micron fibre (under 18.5 microns, often under 16) which is soft enough that most wearers, including some with sensitive skin, find it comfortable. Quality matters: cheap merino is sometimes blended with coarser wool, which feels different.
Is merino processed with chemicals like other fabrics?
The fibre itself needs little chemistry, which is a genuine advantage, but most machine-washable merino is not untreated. To stop it felting and shrinking, it is usually given a superwash treatment: the scales are etched with chlorine, then sealed under a thin polymer resin (Hercosett). That step produces AOX (adsorbable organic halides) in the wastewater, which is why superwash is the least clean part of merino's chain. Untreated, non-superwash merino is cleaner but shrinks if you are careless with it. So merino is not automatically the purest fibre; the finish decides.
Why is merino so expensive?
Three reasons. The supply is limited (merino sheep are concentrated in Australia, New Zealand, and a few other regions). The fibre is graded by micron count and the fine-micron grades cost more. Production is labour-intensive compared to cotton. Expect to pay three to four times what comparable-quality cotton activewear costs.
