Merino vs polyester base layers

A base layer sits against your skin for hours, often while you sweat. Merino and polyester are the two common choices. Here is what independent and industry-funded studies say about each, and where polyester is the better buy.

Bottom line

Merino holds less odor and isn’t plastic, so it doesn’t add plastic fibers when it sheds. Polyester dries faster, costs less and, in one survey, lasted longer. For warmth, studies find little difference between the two.

Head to head

Criterion	Merino wool	Polyester	Which side
Odor^1,2	Wool held the least body odor in a review of wear studies, which ranked wool, then cotton, then polyester.	Polyester was among the fabrics that held the most odor after wear.	Edge: natural
Moisture³	Wool absorbs about 13.6% of its weight in moisture (its “regain”), so it takes up sweat but dries more slowly than polyester.	Polyester absorbs about 0.4%, which is why it dries much faster.	Depends on use
Warmth^4,5	In 21 adults cycling at 8 °C, merino and polyester base layers gave similar core temperatures and comfort.	Same result: a review found most cold-weather studies show no fabric effect, and garment construction matters more.	About even
Durability^6,3	Merino tops often add nylon for strength; KÜHL’s merino crew label says the 5% nylon is “added for durability.”	In a wardrobe survey, synthetic garments were reported to last 6.3 years on average, against 5.3 years for 100% wool.	Edge: synthetic
Microplastics^7,8,9	Wool isn’t plastic. In a 90-day seawater test, wool biodegraded readily (study funded by the wool industry).	Polyester sheds plastic fibers in the wash (about 496,000 per 6 kg load in one lab estimate) and through wear; polyester showed virtually no biodegradation in the same seawater test.	Edge: natural
Cost^10,6,11	Woolx’s 100% merino Explorer Base Layer was $145; KÜHL’s 95% merino crew was $130.	KÜHL’s 100% polyester Akkomplice Crew was $89.	Edge: synthetic
Care³	People wear wool sweaters about twice as long between washes as cotton ones, which means less washing overall (survey funded partly by the wool industry).	Polyester takes up little water, so it dries quickly after washing.	Depends on use

“Which side” is a plain reading of the cited evidence for that row, not a score. Prices are from product pages on October 31, 2026 and change often.

Counterpoints and caveats

Wool has a high climate footprint per kilogram: about 20 kg CO2e per kg of greasy wool in Australian farm studies, mostly from sheep methane. That study was wool-industry funded, and the figure changes up to threefold depending on method.¹²
Natural fibers shed too. Most fibers found in ocean samples are cotton, other cellulose or wool, not plastic.¹³
Several of the merino-side findings (biodegradation, lifespan, washing frequency) come from studies funded by the wool industry. We list them, but say so.^3,9

Short answers

Is merino warmer than polyester as a base layer?

Not measurably, in the studies we found. Adults cycling at 8 °C had similar core temperatures and comfort in merino and polyester base layers.^4,5

Counterpoint: These are small studies; fit and fabric thickness matter more than fiber.

Does merino really smell less than polyester?

Yes, on balance. Wear studies and a review rank odor retention from least to most as wool, then cotton, then polyester.^1,2

Counterpoint: The studies are small and fabric structure also matters, so results vary by garment.

Why choose polyester at all?

It dries faster because it absorbs about 0.4% of its weight in moisture against wool’s 13.6%, it usually costs less, and in one wardrobe survey synthetic garments lasted longer than wool ones.^3,7,8

Counterpoint: Polyester sheds plastic microfibers when washed and worn.

Natural options

Scored brands have a natural-fiber share score; picks pages list specific products from brands with mixed ranges and are not scored.

Minus33Scored brandMerino base layers, scored
IcebreakerScored brandMerino base layers, scored
SmartwoolScored brandMerino base layers, scored
Unbound MerinoScored brandMerino tees and layers, scored
Woolx picksPicks (not scored)100% merino base layers from a mostly blended range

Sources

Industry funding is noted where a study was paid for or co-authored by a fiber industry body or brand. Product labels and prices read October 31, 2026.

1McQueen, Laing, Brooks, Niven (University of Otago). Odor intensity in apparel fabrics and the link with bacterial populations. Textile Research Journal, 2007.
2Laing (University of Otago). Natural fibres in next-to-skin textiles: current perspectives on human body odour. SN Applied Sciences, 2019.
3Laitala, Klepp (SIFO, OsloMet), Henry (QUT). Does use matter? Comparison of environmental impacts of clothing based on fiber type. Sustainability, 2018. Co-funded by Australian Wool Innovation and the Research Council of Norway; lifespan data from an AWI-commissioned survey.
4Cernych et al. (Lithuanian Sports University). Physiological and psychological responses during exercise and recovery in a cold environment is gender-related rather than fabric-related. Frontiers in Psychology, 2017.
5Gavin. Clothing and thermoregulation during exercise. Sports Medicine, 2003.
6KÜHL product page. KÜHL Invigoratr Merino Crew: 95% merino wool, 5% nylon “added for durability”, $130. Product label, read Oct 31, 2026, 2026.
7Napper, Thompson (University of Plymouth). Release of synthetic microplastic plastic fibres from domestic washing machines. Marine Pollution Bulletin, 2016.
8De Falco, Cocca, Avella, Thompson. Microfiber release to water, via laundering, and to air, via everyday use. Environmental Science & Technology, 2020.
9Collie, Brorens, Hassan, Fowler (AgResearch). Marine biodegradation behavior of wool and other textile fibers. Water, Air, & Soil Pollution, 2024. Funded by Australian Wool Innovation; fabrics supplied by Woolmark.
10Woolx product page. Woolx Explorer Base Layer: 100% merino wool, $145. Product label, read Oct 31, 2026, 2026.
11KÜHL product page. KÜHL Akkomplice Crew base layer: 100% polyester, $89. Product label, read Oct 31, 2026, 2026.
12Wiedemann, Yan, Henry, Murphy. Resource use and greenhouse gas emissions from three wool production regions in Australia. Journal of Cleaner Production, 2016. Funded by Australian Wool Innovation.
13Suaria et al.. Microfibers in oceanic surface waters: a global characterization. Science Advances, 2020.

Updated October 31, 2026. More context: Why the label matters · All comparisons