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Wool Underwear in Summer: Why Hikers Wear It in the Heat

Yes, wool underwear works in summer. Merino is thin, breathable and cooling: it pulls sweat away from the skin, dries quickly and does not smell after days on the trail. For hikers that means less luggage, fewer blisters and a drier back on the climb. The key is fabric weight — summer merino is around 150 g/m².

Why does wool make sense in summer at all?

Most people associate wool with winter because they have only met it as a thick jumper or an old thermal set. Summer merino underwear is a different product — a fine knit with the thickness of a T-shirt, weighing less than a pair of socks. The material does not warm you on its own. It regulates temperature by managing the moisture around your skin.

What is the difference between merino and ordinary wool?

Merino wool comes from a sheep breed with an exceptionally fine fibre — around 17–19 microns, against 25–40 microns for conventional wool. The finer fibre bends on contact with skin instead of pricking it. That is why merino does not scratch and can be worn directly against the body with nothing underneath.

How does merino actually cool you?

Merino absorbs moisture into the fibre structure and releases it through evaporation. That process draws heat away from the skin and works like a slow, constant air conditioner. The knit also traps air, which insulates the body from outside heat — the same principle behind covered clothing in desert climates.

What does a hiker gain from merino underwear?

On a day walk the difference is pleasant. On a multi-day trek it becomes functional, and sometimes a safety matter.

  • Two-way temperature regulation — cool on an exposed climb, warm when you stop on a ridge where wind makes it 10 degrees colder.
  • It does not smell — lanolin and fibre structure suppress the bacteria that produce odour. Realistically: three days without washing, no social problem in a mountain hut.
  • Warm when wet — merino keeps part of its insulation even damp, unlike cotton.
  • Fewer blisters and chafing — dry skin under a pack and between the thighs rubs raw far more slowly.
  • Lighter pack — one set instead of three saves weight and space on a long trek.
  • Spark resistant — wool does not melt and is slow to burn, which matters near a fire or a gas stove.

Why is cotton a bad choice in the mountains?

Cotton absorbs up to 27 times its weight in water and does not release it. Once soaked with sweat it stays wet for hours and strips body heat through evaporation — precisely when your body needs that heat most.

Hikers have a saying: cotton kills. It is not dramatic for effect. The classic scenario looks like this: you sweat hard on the climb, reach the ridge, the wind picks up, the temperature drops 8–10 degrees, and a wet cotton shirt cools you toward hypothermia in twenty minutes — even in July.

Merino or synthetic — which is better for summer?

Both beat cotton. The choice depends on trip length and on what bothers you most.

Merino wins when:

  • You are out for several days with no chance to wash
  • Temperatures swing widely — hot in the valley, windy on the ridge
  • You have sensitive skin that reacts to synthetics
  • You will sleep in the same set in a hut or tent

Synthetic wins when:

  • The activity is short and very intense
  • Low cost and abrasion resistance matter most
  • You do not care about odour after four hours

A common compromise many hikers use: merino as the base layer against the skin, with a synthetic or softshell second layer over it.

What fabric weight should I choose for summer?

Fabric weight (g/m²) matters more than the brand name.

  • 120–150 g/m² — summer weight. For hikes from May to September, heat at lower altitude and moderate elevation.
  • 180–200 g/m² — all-round. Works from spring through late autumn and for a night in a hut.
  • 250 g/m² and above — winter thermals. Overkill in summer; it will overheat you.

Practical rule: for a July ascent, take summer-weight underwear and add a light fleece or windbreaker for the ridge, rather than carrying heavier base layers.

Why blend merino with silk?

Pure merino is excellent, but fine summer knits are delicate. Silk threads add strength and a smooth, cool hand feel that makes the fabric more comfortable in direct contact with skin.

A 70% merino / 30% silk blend is a classic summer base layer:

  • Silk is naturally cooling and adds almost no bulk or weight.
  • The fabric becomes softer and glides over skin instead of clinging when you sweat.
  • The blend resists stretching better than 100% fine merino at the same weight.

This is the exact composition we use at Marta Gabarda for the wire-free summer bralette — 70% merino, 30% silk, around €19. We are a small family workshop in Sofia, and the whole range is underwear rather than technical sportswear, which is why the focus is on how fabric behaves against skin over many hours.

How do I choose for a specific route?

A day hike on Vitosha (Cherni Vrah)

You set off in heat and meet wind at the summit. A light merino top or bralette and merino briefs are enough. The main gain is not standing on the peak in a soaked shirt.

A two-day trek in Rila (Seven Lakes or Musala)

A hut overnight and a 15-degree swing between midday and dawn. One set of summer merino covers both days — you wear it at night in the sleeping bag too, where it adds an extra insulating layer.

A multi-day trek (a section of Kom–Emine)
This is where merino shows its real value. Two sets cover five or six days: one worn, one airing on the pack. Merino recovers from odour with a few hours hanging in fresh air.

Specific considerations for women
On a multi-day trek, pack straps run exactly through the underwire zone. So:

  • Choose a wire-free, unpadded bralette — no hard pressure point under the shoulder strap.
  • Look for flat seams in the underbust area.
  • Avoid synthetic lace in friction zones.

How do I care for merino underwear?

Merino is usually ruined by washing, not by wearing

  • Wash at 30 °C on a wool cycle, or by hand.
  • Use enzyme-free wool detergent — standard powders break down the fibre.
  • No fabric softener — it coats the fibre and kills breathability and odour resistance.
  • No tumble dryer, and do not hang wet merino on a hanger — dry it flat so it does not stretch.
  • Between washes, simply air it out — enough in about 80% of cases.

Frequently asked questions

Isn’t it too hot to wear wool in July?

Not at summer weight (120–150 g/m²). Summer merino is thinner than most cotton T-shirts and actively cools through moisture evaporation. The sensation is dryness, not warmth.

Does merino itch?

Fine merino (17–19 microns) does not itch for most people, because the fibre is soft enough to bend on contact with skin rather than prick it. People who remember wool as itchy were usually wearing coarse 30+ micron wool.

Does merino really not smell after several days?

Yes, this is one of its best-documented properties. Wool fibre absorbs odour into its core and limits the environment bacteria need. After three or four days on the trail, merino smells noticeably less than synthetic does after one.

Can I wear merino directly against my skin?

Yes, that is exactly what it is for. Merino works best as a base layer in direct skin contact, because that is where it manages moisture. Wearing a cotton shirt underneath removes almost all of its advantage.

How quickly does merino dry?
More slowly than pure synthetic, faster than cotton — usually a few hours when aired. The important difference is that merino keeps warming you while damp, so drying speed matters less.

Bralette or bra for a woman carrying a pack?

A wire-free bralette. Rigid underwire creates a pressure point exactly under the pack straps and causes pain and chafing on long days. A wire-free merino bralette solves both the pressure and the underbust sweating at once.

Is it worth the price?

Is it worth the price?

Merino costs more per item but replaces several sets on a multi-day trek and lasts years with proper care. For hikers the maths usually works out, because you buy one or two sets rather than ten.

Where can I buy merino underwear in Bulgaria?
Marta Gabarda ships merino and silk underwear across the country with Econt, with cash on delivery. Order online at martagabarda.com or by phone. The atelier is at 205 Alexander Stamboliyski Blvd in Sofia, Monday to Friday, 10:00–17:00.

In short

  • Wool underwear works in summer at fine merino weights of 120–150 g/m².
  • Merino cools by managing moisture, it does not simply add warmth.
  • Cotton is the worst choice for the mountains — wet, it strips body heat.
  • A 70% merino / 30% silk blend adds coolness, smoothness and durability in a summer base layer.
  • For women carrying a pack, a wire-free bralette is the more practical choice.

Marta Gabarda — merino wool and silk underwear made in Sofia, Bulgaria. Questions: office@martagabarda.com

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