Cotton is the most-worn fabric on earth. Merino is one of the highest-performing. Here is the side-by-side that explains why active Kiwis are quietly replacing cotton tees, socks, and base layers with merino.
The seven-point comparison
| Property | Merino | Cotton |
|---|---|---|
| Warmth when dry | High (crimped fibre traps air) | Low to moderate |
| Warmth when wet | Retains most insulating value | Lost almost completely |
| Moisture handling | Wicks vapour from skin; absorbs 30% of weight before feeling damp | Absorbs water; holds it against skin |
| Odour | Naturally antimicrobial; days between washes | Holds odour; needs washing each wear |
| Drying speed | Moderate | Slow |
| Sun protection | UPF 30–50+ naturally | UPF 5–10 typically |
| Biodegradability | Yes | Yes (but conventional growing has high water/pesticide footprint) |
Why "cotton kills" became a tramping rule
The reason every tramping handbook warns against cotton is the wet-warmth gap. A cotton tee that has soaked up sweat or rain will continue to leech body heat for as long as it stays damp. In a temperate climate that's an annoyance. In NZ alpine or shoulder-season conditions, it's a hypothermia risk.
Merino keeps insulating when wet because the air pockets between its crimped fibres remain even after it absorbs moisture. The fabric can hold around 30% of its weight in water before it feels wet to the skin.
The three places merino wins easily
Base layers
Sweat management is the whole job of a base layer, and merino does it dramatically better than cotton. This is the easiest fabric swap in any wardrobe.
Socks
Merino socks reduce blistering, regulate temperature, and stay fresh for days of wear. Cotton socks soak up sweat and stay wet — a recipe for blisters on any walk over an hour.
Travel
One merino tee replaces three cotton tees on a trip. It can be worn three or four times between washes, dries overnight, and packs smaller.
Where cotton is still fine
For sedentary indoor wear in stable temperatures, cotton is genuinely comfortable and inexpensive. There is no need to replace your weekend movie-watching tee with a merino one. Cotton's weakness is exposure to moisture and temperature change — not indoor life.
The rule of thumb: if you might sweat, get cold, or get wet — wear merino. If you definitely won't — wear what you like.
Frequently Asked Questions
Why do trampers say cotton kills?
Wet cotton has almost no insulating value, so a sweat- or rain-soaked cotton layer in cold conditions accelerates heat loss.
Is merino warmer than cotton?
Yes — the crimped fibre traps warm air, and merino stays warm when wet.
Is merino more sustainable than cotton?
It depends. Conventional cotton uses huge amounts of water and pesticides. Merino is renewable and biodegradable but carries methane impact.
Can merino replace cotton for everyday wear?
Yes. A 150 or 200gsm merino tee is a direct replacement.
Replace One Cotton Tee
Start with a single 200gsm merino tee. The everyday-wear difference is immediate.
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