The base layer is the most important item in your clothing system, it sits next to your skin and determines how comfortable you are across the whole day. Get it wrong and no amount of expensive outer layers will compensate.

The principle is simple: the base layer manages moisture. When you’re working hard, you sweat. A good base layer wicks that sweat away from your skin and moves it outward, where it can evaporate. A bad base layer (cotton, or any fabric that absorbs and holds moisture) gets wet and stays wet, which chills you rapidly when you stop.

Here’s what we recommend for UK hillwalking.

Best Base Layers for UK Hiking

Icebreaker Merino 200 Oasis: Best Merino All-Rounder

RRP: ~£85 (top) | View on Amazon UK

The 200 Oasis is the base layer most UK hillwalkers end up at after trying others. The 200gsm merino weight hits the sweet spot for three-season British conditions, warm enough for cool days and working on ascents, not so heavy that it’s uncomfortable in summer. The 100% merino construction offers excellent odour resistance and a comfortable, non-scratchy feel against the skin.

Icebreaker’s construction quality is consistent across their range. The flatlock seams don’t cause chafing on long days. The fit is slim without being restrictive. Available in crew neck and half-zip, the half-zip is worth the extra for venting on steep climbs.

Pros: Excellent moisture management, superb odour resistance, comfortable Cons: More expensive than synthetic, slower to dry after washing Best for: Multi-day trips, three-season hillwalking, those who run cool

Smartwool Classic All-Season Merino: Best Value Merino

RRP: ~£70 (top) | View on Amazon UK

Smartwool’s All-Season layer uses a Merino-nylon blend (87% merino, 13% nylon) that adds durability to the natural properties of merino wool. The result is a base layer that resists pilling better than pure merino and stands up to the kind of repeated use a hillwalking base layer gets.

Performance across three seasons is excellent. Warmth-to-weight is good; moisture management is natural merino quality. Slightly more affordable than Icebreaker at equivalent quality.

Pros: Durable merino blend, excellent three-season performance, good value Cons: Nylon blend slightly less soft than pure merino Best for: Regular hillwalkers, those who want merino durability

Patagonia Capilene Cool Lightweight: Best Synthetic Option

RRP: ~£55 (top) | View on Amazon UK

For those who prefer synthetic or want a summer-specific base layer that dries faster than merino, Patagonia’s Capilene Cool Lightweight is the benchmark. The double-weave construction moves moisture rapidly and cools by evaporation, noticeably effective in warm conditions and during intense effort.

Patagonia uses recycled polyester throughout the Capilene range, and the garments are fair trade certified. It’s one of the better-made synthetic base layers on the market. The odour resistance is better than most synthetics (treated with HeiQ Fresh), but still below merino.

Pros: Fast drying, excellent evaporative cooling, ethical manufacturing Cons: Odour retention worse than merino on multi-day trips Best for: Summer hillwalking, high-output activities, hot walkers

Montane Dart Zip Neck: Best Technical Synthetic

RRP: ~£60 (top) | View on Amazon UK

Montane’s Dart range uses lightweight Vapour-Rise polyester with a zoned construction, lighter mesh panels under the arms and across the back where you sweat most, heavier fabric across the chest. This targeted approach improves moisture management compared to a single-fabric base layer.

The quarter-zip neck is useful for venting on steep ascents. The slim fit works well under any mid-layer without bunching. Slightly more technical in its design than the Patagonia Capilene, and well-suited to fast and light hillwalking.

Pros: Zoned moisture management, quarter-zip vent, well-designed for active use Cons: Higher price for synthetic Best for: Fast hikers, technical routes, those who prioritise moisture management

Decathlon Forclaz MT500 Merino: Best Budget Merino

RRP: ~£35 (top) | View at Decathlon

Decathlon’s in-house technical brand produces merino base layers at a price point that undercuts the premium brands significantly. The Forclaz MT500 uses 140gsm merino, slightly lighter than ideal for cold conditions but perfectly adequate for active summer and early autumn use. Odour resistance and moisture management are both as good as merino physics allows.

The durability is lower than Icebreaker or Smartwool, and the fit is slightly roomier than some walkers prefer. But for £35, it delivers genuine merino performance and makes a good introduction to merino base layers.

Pros: Merino performance at an accessible price, good value for beginners Cons: Less durable, lighter weight suits warmer conditions only Best for: Beginners, budget-conscious walkers, summer use

Base Layer Fit and Care

Fit

A base layer should fit close to the skin, not tight enough to restrict movement, but without excess fabric that bunches under a mid-layer or drags moisture away from your skin inefficiently. A slim or athletic fit is the standard recommendation.

Check sleeve length on long-sleeve versions: the cuff should reach your wrist without pulling up when you reach. This keeps a continuous moisture-wicking surface from shoulder to hand.

Layering

The base layer works as part of a system. Its effectiveness depends on having a mid-layer that keeps it close to your skin on cold days, and a shell layer that allows moisture to pass outward in wet conditions. A waterproof shell that traps moisture will reduce your base layer’s effectiveness regardless of its quality.

Washing

Wash base layers after every use or every two days of use on multi-day trips. Dried sweat degrades synthetic fibres and reduces the odour-managing properties of merino over time. Follow garment-specific care instructions, merino especially requires gentle washing.