Base layers for hillwalking: which of ours to choose

By Kenny Stocker 30 Aug 2022 8 min read

Merino for steady walks and multi-day trips, a blend for heavy packs, synthetic for fast walking. Our four hillwalking base layers compared.

We make four base layers for hillwalking. Which suits you comes down to how hard you walk and how long you're out:

For steady hillwalking, cold days and trips where you can't wash: Kepler
For long days with a heavy pack: Aztec
For fast walking and hard climbs where you sweat a lot: Koulin
For warm, easy walks and travel: Picu

The one thing worth knowing before you choose: merino evens out your temperature between climbs and stops and goes days without smelling, while synthetic gets rid of sweat fastest. Our merino or synthetic base layer guide explains how each fabric works.

Kepler: merino for steady walking and multi-day trips

Kepler is 100% ultrafine merino at 17.2 micron, in a 160gsm fabric. It's the one to choose if comfort on a long, stop-start day matters most.

Comfortable from the climb to the summit. Merino takes up sweat as vapour and evens out your temperature, so you're less clammy going up and less chilled when you stop.
Goes days without washing. Merino handles odour much better than polyester, which is what you want on a hut-to-hut walk or a wild camp.
Soft against your skin. Ultrafine fibres don't itch, and flatlock seams sit flat under rucksack straps.

Best for: steady-paced hillwalking, cold days and multi-day trips. It dries slower than synthetic, so it's less suited to hard efforts on warm days.

Kepler is made from non-mulesed merino certified to the Responsible Wool Standard.

Men's Kepler Long Sleeve merino base layer

Women's Kepler Long Sleeve merino base layer

Men's Kepler Long Sleeve and women's: the all-rounder.

Men's Kepler Short Sleeve merino base layer

Women's Kepler Short Sleeve merino base layer

Men's Kepler Short Sleeve and women's: for warmer days.

Men's Kepler Zip Top: a quarter zip to vent on the climbs, a high collar against draughts, and thumb loops to keep the sleeves in place.

Men's Kepler Long Johns merino base layer

Women's Kepler Leggings merino base layer

Men's Kepler Long Johns and women's Kepler Leggings: for winter walking, under your trousers. They use corespun merino, a stretchy core wrapped in merino, so they keep their shape.

Aztec: merino blend for long days under a pack

Aztec is half merino and half recycled polyester, in a light 140gsm corespun fabric. Choose it if pure merino wears out or dries too slowly for you.

Tougher under pack straps. The polyester core makes it harder wearing than pure merino.
Dries faster than pure merino. Useful on long, sweaty days and wet ones.
Still resists odour. You can wear it for days, like Kepler.

Best for: long days with a heavy pack, multi-day walks and anyone who finds pure merino too delicate.

Aztec uses non-mulesed, RWS-certified merino and GRS-certified recycled polyester.

Men's Aztec Long Sleeve and women's.

Koulin: synthetic for fast walking and hard climbs

Koulin is our do-it-all synthetic base layer, in 100% recycled polyester. Choose it if you walk fast, sweat a lot or want something tough and easy to wash.

Gets rid of sweat fastest. The fabric wicks sweat away from your skin, and mesh panels under the arms and across the back let heat out.
Wear it more between washes. It's treated with Polygiene to slow odour building up.
Handy details. Flatlock seams, a relaxed fit that also layers under a fleece, and a small rear pocket with a key clip.

Best for: year-round UK hillwalking at a good pace, fast summer days and hard climbs.

Men's Koulin Trail Tee synthetic base layer

Women's Koulin Trail Tee synthetic base layer

Men's Koulin Trail Tee and women's.

Men's Koulin Trail Long Sleeve synthetic base layer

Women's Koulin Trail Long Sleeve synthetic base layer

Men's Koulin Trail Long Sleeve and women's.

Picu: cotton feel for easy walks and travel

Picu isn't a technical base layer in the same way as the other three. It's a tee in recycled polyester and organic cotton that looks and feels like cotton but dries about four times faster.

Feels like your favourite t-shirt. Soft, with articulated sleeves and a little stretch.
Dries much faster than cotton. The drirelease fabric moves sweat away and dries quickly.

Best for: summer valley walks, pub-to-pub routes, travel and days when you're not working hard. On a cold or wet hill day, choose Kepler, Aztec or Koulin instead.

Men's Picu Long Sleeve and women's.

Our hillwalking base layers compared

Range	Fabric	Drying	Feel	Best for
Kepler	100% merino, 160gsm	Slower	Soft, never itchy	Steady walking, cold days, multi-day trips
Aztec	50% merino, 50% recycled polyester, 140gsm	Faster than pure merino	Soft	Long days under a heavy pack
Koulin	100% recycled polyester	Fast	Smooth, technical	Fast walking and hard climbs
Picu	Recycled polyester and organic cotton	About 4x faster than cotton	Like a cotton tee	Easy walks and travel

How to choose for the way you walk

How hard you walk. If you keep a steady pace with plenty of stops, merino (Kepler) keeps you most comfortable. If you push hard and sweat a lot, synthetic (Koulin) gets rid of it fastest. Aztec sits between the two.

How long you're out. On a day walk, any of the four works. On a multi-day trip, merino or the Aztec blend, because you can wear them for days without them smelling.

The season. In winter, a Kepler long sleeve with long johns or leggings under your trousers. In summer, a Kepler or Koulin tee, or a Picu for easy days.

The trade-off with pure merino is toughness and drying time: it can wear through under pack straps and dries slower than synthetic. If that's put you off merino before, try Aztec. Whatever you choose, it's the first layer of three. See layering for hillwalking for what goes over the top.

See all men's and women's base layers, or just the merino base layers.