Sonder Bikes
Baselayers are key to warmth and comfort. Learn how materials, fit and layering systems help you stay dry and warm on hillwalking adventures.
Your base layer is the foundation of comfortable hillwalking. Get it wrong and you'll be clammy on the climb, then chilled at the summit. Get it right and you'll barely notice it's there.
We make four base layer ranges, each suited to different hillwalking styles and conditions. This guide helps you choose the right one.
Quick Guide
Koulin: The Versatile Hillwalking Base Layer
Our do-it-all base layer tops for wearing alone or as part of a layering system. Made from wicking polyester with mesh panels for increased breathability under layers.
Why Hillwalkers Choose Koulin
It's incredibly versatile. The recycled polyester fabric is durable under rucksack straps and shrugs off contact with rock. Mesh panels under your armpits increase breathability in a key area when wearing under layers. There's also a small stash pocket for your car key.
Best For
Year-round hillwalking in the UK. With short and long-sleeved, round-neck and zipped neck options, you can match the Koulin to the season and your personal preference.
Is it sustainably made?
As well as making these base layers with 100% recycled materials, we’ve used Polygiene(R) anti-odour treatment. This increases the number of times you can wear your tee before needing to wash it, making your tee last long and reducing its footprint over time.
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Vayper: Fast-Drying Base Layer for High-Output Hillwalking
A true next-to-skin base layer made from ultralight recycled polyester and treated with Polygiene(R) for better odour-resistance. Designed to move sweat away as quickly as possible to keep you cool and dry whilst working hard.
Why Hillwalkers Choose Vayper
The Vayper's tight, athletic cut helps draw sweat away from the skin faster, and the ultrafine material is incredibly fast-drying. It fits neatly under fleeces and shells, trapping a thin layer of warm air next to the skin.
Best For
Fast-paced hillwalking where you're generating lots of heat and sweat. The close fit works well under multiple layers, and the rapid drying time keeps you comfortable during sustained efforts on steep ground.
Is it sustainably made?
We’ve used a fabric made from 100% post-consumer recycled polyester, reducing our dependence on virgin polyester, and the Vayper is also Polygiene(R) treated to reduce washing.
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Kepler: Merino Wool Base Layer for All-Day Comfort
Our merino wool tops use 100% ultrafine 17.5 micron merino wool fibres: extremely soft on the skin, naturally breathable and odour-resistant with a fantastic warmth-to-weight ratio.
Why Hillwalkers Choose Kepler
The ultrafine merino wool fibres are softer next-to-skin, dry quicker and have a higher warmth-to-weight ratio than heavier fibres. Wool is naturally breathable (transporting sweat vapour through its fibres) and has clever properties that keep you cool in the heat and warm in the cold.
Best For
Steady-paced hillwalking and multi-day trips. It's not as fast-drying as synthetic base layers, so is less suited to high-intensity efforts in warm conditions. But wool's incredible odour resistance means you can wear the Kepler for days without it getting unpleasant - ideal for hut-to-hut walks or wild camping.
Is it sustainably made?
We only use merino wool from non-mulesing sources. Mulesing is a cruel and unnecessary practice used by some farms to reduce labour costs and increase profits. Wool is a completely natural and sustainable material and its natural odour-resistance means it requires very little washing, (usually a quick air on the line will do), reducing its footprint.
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Picu: Cotton-Feel Base Layer for Relaxed Hillwalking
A fast drying and wicking poly-cotton tee designed to feel as comfortable next to the skin as a cotton t-shirt.
Why Hillwalkers Choose Picu
The blend of organic cotton and drirelease(R) branded polyester results in a really soft-feel tee that wicks and dries almost as quickly as polyester - around 4x faster than pure cotton.
Best For
Lower-level walks and gentle hillwalking where you want comfort without looking overly technical. The Picu works well for summer valley walks, pub-to-pub routes, and days when you're not pushing hard enough to generate heavy sweat.
Is it sustainably made?
The Picu uses Drirelease Eco fabric made from organic cotton and 100% recycled polyester.
Your Base Layer is Just the Start
The tried and tested layering system for hillwalking consists of three layers designed to work together.
Base layer - Your next-to-skin layer. Moves sweat away from your skin to reduce that clammy feeling and prevent chills when you stop.
Mid layer - Your insulation. Traps warm air to keep you comfortable. Fleeces are the hillwalker's go-to choice.
Outer layer - Your protection from wind and rain. A breathable waterproof is essential for UK hillwalking.
Read our complete guide to layering for hillwalking to understand how these layers work together.
Hillwalking Layering Series
Explore our complete guides to each layer of the hillwalking system:
- Best Layering Systems for Hillwalking - The complete overview
- Comfortable Midlayers for Hillwalking - Fleece and wool options for warmth
- Best Insulated Jackets for Hillwalking - Down and synthetic options for cold days
- Best Waterproof Jacket for Hillwalking - Protection from wind and rain
- Best Hillwalking Trousers - Legwear for all conditions
- Best Hiking Socks - Foundation layer for comfort and durability
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