The best base layers 2024: the foundation of your hiking garb

Collage of the best base layers
(Image credit: Future)

As the foundation of your layering system, the best base layers provide comfort and warmth during harsh conditions and can also be worn solo when the weather heats up. A base layer is worn next to your skin, so it's important that your base layer feels comfortable, manages your temperature effectively, wicks moisture away and moves with you.

Many of the best base layers are made from natural materials, such as Merino wool or bamboo, or are created using synthetic materials, usually polyester. Hybrids are very common too, combining the insulation of something like Merino with the fast drying qualities of polyester and the stretchiness of elastane.

We've ventured into all kinds of conditions to bring you this definitive guide to the best base layers available in 2024. The Icebreaker 200 Oasis Long Sleeve Crewe Thermal Top is our highest rated base layer here. Its Merino wool content makes it super comfortable and the performance is second to none. We kick things off with this and other Merino tops, before moving on to blended options, synthetic tops and bamboo base layers.

The quick list

This is our quick list, a brief overview of the best base layers available. To delve deeper into the specifics of each garment, see our more detailed reviews further down the page in this guide.

The best base layers we recommend in 2024

You can trust Advnture Our expert reviewers spend days testing and comparing gear so you know how it will perform out in the real world. Find out more about how we test and compare products.

The best base layer overall

Icebreaker 200 Oasis Long Sleeve Crewe Thermal Top base layer

A stylish, versatile, mega-comfortable all-Merino base layer (Image credit: Icebreaker)
Stylish, versatile and comfortable, this pure merino top performs well even when wet

Specifications

Gender availability: Men's & women's
Materials: Merino wool
Weight (Male large): 263g/9.3oz
Sizes: Men's S-XXL / Women's XS-XL
Colors: Black, navy, heather gray and more
Best for: Hiking, biking, trail running, and climbing

Reasons to buy

+
Super comfortable
+
High performing and odor resistant
+
Keeps working when wet

Reasons to avoid

-
Expensive at more than $90
-
Won’t last as long as synthetic tops
-
No thumb hoops

The Oasis – weighing in at 200 grams square meter (gsm) – is an ideal thickness for a base layer, and unsurprisingly is one of the company’s best selling garments. Made from 100% Merino wool, we found this top to be supremely comfortable. On test, it wicked moisture away with aplomb and maintained most of its thermal properties when wet. It's also naturally antimicrobial, and therefore odor-resistant. 

It performed equally well for chilly trail running and trekking outings, and during a mid-winter sea paddle, though we would have appreciated thumb loops to keep the sleeves in lace.

As a natural material, Merino wool is biodegradable, and the dye used is plant-based and ethically sourced. Icebreaker has never been a bargain brand, and this isn’t a cheap top. The simple designs are cheaper, but for a little extra cash there are funkier prints available too.

Read our full Icebreaker 200 Oasis Long Sleeve Crewe Thermal Top review

The most stylish Merino base layer

Artilect W-Flatiron 185 Crew Td Tie Dye base layer

A very warm yet lightweight base layer for winter adventures (Image credit: Emily Woodhouse)
Ideal for cold winters, this super-stylish base layer is lightweight with great coverage

Specifications

Gender availability: Male/female
Materials: Nuyarn (Australian merino wool)
Weight: 185 GSM
Sizes: XS to XL
Colors: green/gold tie-dye
Best for: Snow and mountain adventures

Reasons to buy

+
Excellent thermal properties
+
Long cut and thumb loops
+
Lovely soft feel
+
Flatlock seams are very comfortable
+
Merino has antibacterial properties

Reasons to avoid

-
Can be too hot

The Artilect W-Flatiron 185 Crew tie-dye base layer (the men's version is the M-Flatiron) may be sold as ‘warmer’, but it is actually a very hot winter base layer. Designed with Nuyarn merino fabric, it exhibits all of merino’s natural properties, but these are amplified thanks to a twist-free fibre construction. On test, we found the cut to be long in the arms and high in the neck, with thumbholes that prevented the top riding up beneath mid layers and kept our wrists extra cosy. 

The base layer top has gusseted underarms with breathable panels that extend from waist to wrist. Despite having several connected panels, the seams are all flatlock stitched, meaning there is no chafing and barely an awareness that the seam is there at all. It's definitely one of the most comfortable base layers we've tested.

The tie-dye color scheme is very distinctly Artilect and it’s refreshing to see more brands step away from the standard black base layer (even though that's something of a moot point when it's covered up under a fleece and jacket).

Read our full Artilect W-Flatiron 185 Crew Td Tie Dye base layer review

The best lightweight Merino base layer

Salewa Zebru Responsive Long-Sleeve Top

Super light base layer that's cleverly designed and surprisingly snug (Image credit: Salewa)

3. Salewa Zebru Responsive Long-Sleeve Top

Exceptionally light and high performing

Specifications

Gender availability: Male/demale
Materials: Alpine wool (83%) and manmade poly
Weight (Male large): 170g / 6oz
Colors: Blue, gray, green and more
Best for: Hiking, biking, trail running, climbing, alpine adventures

Reasons to buy

+
Very light
+
Body hugging design
+
Flat-lock seams
+
Doesn't restrict mobility

Reasons to avoid

-
No thumb hoops

Named for Monte Zebrù in the Ortler Alps, this top is exceptionally light, but it punches well above its weight when it comes to performance. The majority-merino material offers everything that wool always brings to the party – breathable with excellent moisture-wicking capability, the ability to keep you warm when its cold and cool when it’s hot, natural odor resistance – but there is much more going on here.

The Zebru a figure-hugging bodymapped design, woven with ‘Responsive’ smart synthetic yarns including natural thermoreactive minerals that (according to Salewa) can absorb far-infrared radiation (FIR) from your body, and slowly release it back into muscle tissue, leading to better blood flow, improved oxygenation, longer-lasting warmth, enhanced performance and faster recovery. 

This all sounds very impressive, even if it is impossible to monitor, but having tested this top on the trails, we can attest to its excellent performance. It's a tight-fitting base layer, but the four-way stretch material means you can move easily while wearing it, and the next-to-skin comfort levels are good, with flat-lock seams causing no rubbing or annoyance. It is also styled long, so it doesn’t ride up your back, but disappointingly it lacks thumb hoops.

The best hybrid base layer overall

best hiking boots: Matthew Jones

This midweight base layer delivers versatile warmth for cooler conditions (Image credit: Matthew Jones)
Odor-resistant, soft and comfortable, the Rho Hybrid combines the benefits of synthetic fibers and natural merino wool

Specifications

Gender availability: Male/female
Materials: Polyester/nylon/wool blend
Weight: 170g/6oz
Colors: Gray, black, red
Best for: Winter hill and mountain hiking

Reasons to buy

+
Particularly warm
+
Wicks moisture fast
+
Soft and comfortable
+
Great fit
+
Odor-resistant

Reasons to avoid

-
No thumb loops
-
Costs over $100 (although see our deals for cheaper)
-
No women’s version yet

With the Rho Hybrid, Arc’teryx have attempted to give you the best of both worlds offered by natural and synthetic fibres. The main fabric is their Phasic AR II, a midweight polyester that has been treated with silver ions to neutralise body odor, but there are also zoned panels under the arms made from a blend of natural merino wool and hard-wearing nylon. We discovered that the result is a hybrid design that does its job really well – a top that supplies great wicking performance, comfort and warmth, without any unpleasant odor.  

It also happens to have one of the best fits of any long-sleeved technical tee we’ve tested. It has plenty of length in the arms and torso, plus a stand-up collar that does a great job of preventing chills from creeping down your neck. The cut is trim enough to feel cosy without being skin-tight, unlike a lot of other compression-style winter layers out there. The deep neck zip is a great way to dump a little extra heat if you’re working hard uphill too. The fabric is soft and comfortable, with very thin, flatlock seams to avoid irritation.

It’s tempting to go cheap on your base layers – after all, they’re not generally the most exciting bits of kit. But we think a top-quality technical layer like this one is well worth it.

Read our full Arc’teryx Hybrid Half Zip base layer review

The best hybrid base layer for warmth

Helly Hansen Lifa Merino Mid-weight Hoodie

A hardcore 2-layer hoodie from Helly Hansen, perfect for full-on adventures in the cold zone, or just as a nice looking top to hang in (Image credit: Helly Hansen)
This two-layer hoodie is super-warm and great value for money

Specifications

Gender availability: Male/Female
Materials: Merino/polypropylene blend
Weight: (Male large): 330g/11.6oz
Colors: Black, navy blue, lavender
Best for: Winter hill hiking, skiing and alpine adventures

Reasons to buy

+
Great value for performance level 
+
Extremely warm
+
Hood for extra protection

Reasons to avoid

-
Too warm for some conditions
-
Relatively heavy at 330g
-
No thumb hooks

Helly Hansen pretty much pioneered the concept of technical, high-performing base layers and they remain industry leaders when it comes to making good stuff that will keep you alive in challenging conditions, as the double-layer Lifa Merino Hoodie perfectly illustrates. ‘Lifa’ is the brand’s own high-performing polypropylene yarn, which is used in almost equal measure here with merino wool. On test, we found that both fabrics excel at doing all the things we'd want a base layer to do – they wick moisture away from the body and have excellent thermal qualities even when wet – but each also brings its own tricks to the party. 

The merino brings with it natural antibacterial and anti-odor properties, while the Lifa is more hard-wearing and helps keep the top in shape. A really comfortable top, with flat seams, this is the only base layer on test that had a hoodie, which people will either love or hate. If you’re out and about in seriously cold conditions, your ears are going to love it – it fits under climbing or bike helmet no problem, and really adds to the protection level of the top, making it suitable for high level epics on serious mountains. If you’re adventuring at a more modest level, this is still a lovely top, but you might find it a little too substantial to wear as a base layer.

Read our full Helly Hansen Lifa Merino Mid-weight Hoodie review

The best hybrid base layer for breathability

best base layer: Smartwool Women’s Merino Sport Long Sleeve top

A breathable, fast-wicking, long-sleeved-but-loose-fitting merino top that feels oh-so-soft against the skin and can be worn as a base layer or a midlayer (Image credit: Jessie Leong)
A lightweight, comfortable and warm base layer that's ultra breathable and fast drying

Specifications

Materials: Merino wool (53%) and Tencel Lyocell (47%)
Weight (medium): women's: 110g / 3.88 oz; men's: 138g / 4.86 oz
Colors: women's: Twilight blue/ Light grey heather / Festive fuschia / Bleached aqua heather; men's: Charcoal heather / Picante / Light Neptune blue
Compatibility: Hiking, backpacking, mountaineering, trail running, snow sports and yoga

Reasons to buy

+
Light, comfortable & warm
+
Precise fit, designed with active movement in mind 
+
Ultra breathable with fast-drying moisture management
+
Thermo-regulation for high intensity activities in cold conditions

Reasons to avoid

-
More loose-fitting than most base layers
-
Expensive
-
No thumb hoops
-
Hand wash advised

Combining strict ethical production standards and technical functionality is a hard task, but the Smartwool Women’s Merino Sport Long Sleeve Top delivers on both fronts. Proudly boasting ZQ certification, not only does it feel good from a consumer perspective but the top also performance perfectly. 

The Merino Sport Long Sleeve top’s Tencel Lyocell fibres are comprised of composite recycled cellulose, making the garment, lightweight and super comfortable for a range of different active sports. Temperature regulation, odour resistance, and moisture management are all key features why many people opt for merino – but with this top users don’t suffer with the ‘damp  wool top feeling’ that you can sometimes experience with the material, thanks to this high-performing, recycled cellulose fibre. On test, we found it feels nice against the skin, helps minimise awkward sweat patches and makes the garment ideal for wear in-between temperature fluctuations. This is a product for all seasons. 

Our tester felt the sizing was somewhat generous, with extra room on the waist and arm length; she reports that a small felt more like a size 12 – so this is worth bearing in mind if you’re after a more fitted top.

Read our full Smartwool Women’s Merino Sport Long Sleeve top review

The best value hybrid base layer

Rab Forge Long-sleeved Tee

Lightweight, high-performing technical tee for warmth all year round (Image credit: Rab)

7. Rab Forge Long-sleeved Tee

A high-performing, lightweight top that's odor-resistant and great value

Specifications

Gender availability: Male/female
Materials: Merino/polyester blend
Weight (Male large): 178g/6.3oz
Colors: Blue, black, red and more
Compatibility: Hiking, biking, trail running, climbing, alpine adventures

Reasons to buy

+
Lightweight at 178g
+
High performing
+
Odor-resistant 
+
Moisture-wicking

Reasons to avoid

-
No thumb hoops

Made from a magical mix of merino and manmade polyester (32% of which is recycled), this simple-looking top is a lightweight, high-performing base layer that did everything we could have asked it for during the test period. The athletic-fit Forge kept us warm (even when wet), dried quickly, wicked moisture, refused to stink even after extended wear and kept its shape.

It will serve you well out on the trails all winter, worn as an active undergarment, but at this weight, it’s one of those pieces of kit that’s well worth stashing in a backpack (or even a hydration pack) all year round, in case a change of conditions catches you out and you find yourself in need of an extra layer. The only thing it is missing is thumb hoops, to stop the top riding up your arm when you pull on another layer.

The best synthetic base layer overall

Páramo Grid Technic base layer

A dynamic two-in-one top capable of keeping you warm – or cool (Image credit: Páramo)
Superb performance at a very low weight, this can be worn all year round

Specifications

Gender availability: Male/female
Materials: Polyester
Weight (Male large): 238g/8.4oz
Colors: Gray, green, red and more
Best for: Hiking, biking, trail running, climbing, alpine adventures

Reasons to buy

+
High neck with zip
+
Thumb hoops
+
Long back
+
Ethically made and recyclable

Reasons to avoid

-
Not quite as comfy as merino
-
Can accumulate body odor over time

The polyester-based Parameta G material used to make this well-thought-through top features an ingenious raised-grid pattern that, when another layer is added on top, traps air between the squares. This air then becomes warmed by your body heat, providing a layer of thermal insulation. Clever. On test, if we ever got too hot, we could quickly release this air by taking off (or just unzipping) a mid layer or outer layer. Alternatively, in warmer conditions or during high intensity activity, the Grid Technic can be worn on its own, when it works as a standard poly top, providing decent levels of warmth (even when wet) and excellent moisture wicking properties. 

The Grid Technic has a high neck to keep your throat warm, which features a mid-length zip (with a good chin protector), so you can let cool air in when needed. It also has thumb hoops, so the base layer won’t ride up your arm when you pull another layer over the top, and your wrist won’t become exposed between the top and your glove. You shouldn’t suffer a chilly lower back, either, even when wearing a backpack, as the top is longer at the rear. The athletic cut means it fits closely (no annoying excess material flapping around) and the next-to-skin comfort is good, if not quite as luxurious as merino. As with the vast majority of Páramo garments, this top is made ethically in Colombia with the Miquelina Foundation, a member of the World Fair Trade Organization, and it is fully recyclable through Páramo.

Read our full Páramo Grid Technic base layer review

The best recycled synthetic base layer

A man stands wearing a Saxx Roast Master Mid-Weight Long Sleeve base layer, the sea and sky behind him

A sustainable base layer that keep you warm even when wet (Image credit: Pat Kinsella)
A super-comfortable base layer made from recycled plastic and pulped wood

Specifications

RRP: $75 (US) / £65 (UK)
Materials: Recycled polyester (87%), Tencel lyocell (9%) & elastane (4%)
Sizes: S–XXL
Colors: Black / Dark Brick / Twilight / Get Out Camo
Compatibility: Hiking, trekking, backpacking, mountaineering, trail running, snow sports and camping

Reasons to buy

+
Very comfortable, with flat seams
+
Warm
+
Wicks moisture
+
Retains thermal properties when wet

Reasons to avoid

-
No thumb hoops
-
Sizes quite large
-
Might accumulate smells over time

Produced by US brand Saxx, which specialises in making men’s underwear that provides comfort during active pursuits, the Roast Master long-sleeved top is a midweight base layer designed for cool weather use by hikers, bikers, runners, skiers, boarders, paddlers, climbers and campers. The material mix is predominantly recycled synthetics, combined with Tencel lyocell, an eco-friendly fabric where the fibre content is derived from sustainable wood, and elastane is also used to provide some stretch, so the top won’t inhibit your movements on the hillside, mountain top, water or crag. 

Our tester reported that: "While I never felt my movement was impacted or restricted by the top, the degree of stretch is not as pronounced as in some base layers I’ve tested… [and] despite Saxx saying it’s a slimfit garment, I found the Roast Master to be slightly over-generously sized." So, if you prefer a body clinging base layer, choose a size smaller than usual. The material is breathable, wicks moisture away from your skin, will continue to work and provide thermal protection even when damp, and it dries extremely quickly. Saxx says this garment has been treated with an anti-stink product, but only time will tell if this works. The flat seams and soft-finish inner make it exceptionally comfortable to wear, and it should last for many seasons. Our main criticism of this top, beside the sizing issue, is the lack of thumb loops. 

The best synthetic base layer for dynamic movement

Columbia Men's Omni-Heat 3D Knit Crew II Base Layer Shirt

A space-age base layer full of technology to keep you toasty (Image credit: Columbia)
Great performance from spage-age technology

Specifications

Gender availability: Men's & women's
Materials: Polyester/elastane
Weight (Male large): 232g / 8.2oz
Colors: Black/blue
Best for: Skiing, snow-boarding, alpine adventures and cold-weather hiking, biking and trail running

Reasons to buy

+
Uses superior tech to keep you toasty
+
Smart thumb loops
+
Four-way stretch material for active use
+
Maintains thermal properties when wet

Reasons to avoid

-
Too warm for some conditions
-
No zip to dump warm air if you overheat
-
All synthetic materials

Although it has a pretty pedestrian appearance when being worn, if you turn this top inside out, it looks almost metallic, and resembles something you might see worn on the bridge of the starship Enterprise. As with everything they make these days, Columbia have employed their trademark Omni-Heat technology in this base layer, in a bid to keep the wearer warmer than any other brand. The Omni-Heat concept involves the use of loads of soft fiber pods, which create a little gap between the garment being worn, and your skin – your body heat then warms the air trapped inside this space, and the silver lining of the top reflects this heated air back at you. Genius.

In addition, because there’s a space between your body and the base layer, less moisture builds up, and the poly fabric of the top wicks sweat away too. This all sounds impressive, but it does actually work too – in fact, it worked so well on test that we could often feel pretty hot in this top, although shedding an outer layer generally sorts that out. If you’re heading somewhere seriously cold – like a mountain top, or a ski resort – this is a great option.

Read our full Columbia Omni-Heat 3D Knit Crew II base layer shirt review

The best sustainably-made synthetic base layer

Craghoppers First Layer Long-Sleeved T-Shirt base layer

No nonsense base layer, made from recycled plastic bottles (Image credit: Craghoppers)

11. Craghoppers First Layer Long-Sleeved T-Shirt

This recycled base layer will keep you warm even when wet

Specifications

Gender availability: Male / Female
Materials: Recycled polyester (77%) and viscose (23%)
Weight (Male large): 230g / 8.1oz
Sizes: Men’s: S–XL; Women’s 8–20
Colours: Men’s: Deep blue / Steel blue / Navy; Women’s: Winter rose / Mountain green / Charcoal stripe
Compatibility: Hiking, biking, trail running, climbing, alpine adventures

Reasons to buy

+
Good thermal properties, even when wet
+
Made from recycled bottles
+
Durable
+
Costs just £35

Reasons to avoid

-
More likely to hold odors
-
No thumb hoops

At first glance, this thermal top looks fairly basic – it’s here to do a job for a fair price with no bells and whistles, true enough – but there’s more of a backstory to these base layers, because they are made from recycled plastic. Around 10 to 12 discarded bottles go into each garment, and while we know microfibres still get released every time synthetic tops are washed, it’s certainly better to buy something recycled. Craghoppers’ sustainability policies are solid, and the brand also guarantee their garments for life (as in, the clothes expected lifespan), and will take used garments back to recycle them once they’ve been worn out.

A relatively thick top, we found its performance levels were excellent: in our tests it kept us warm, wicked moisture away, and absorbed very little water, letting it keep its warmth-giving capabilities even when wet. On the down side, it lacks thumb hoops, but it is available in a short-sleeve iteration, for year-round use.

Best base layers comparison table

Swipe to scroll horizontally
Base layerList priceWeightMaterialsCompatibility
Icebreaker 200 Oasis Long Sleeve Crewe Thermal $95–$110 (US) / £75–£100 (UK)263g/9.3ozMerino woolHiking, biking, trail running, climbing, alpine adventures
Artilect W-Flatiron 185 Crew Td Tie Dye$150 (US) / £110 (UK) / €130 (EU)185 GSMNuyarn (Australian merino wool)Snow and mountain adventures
Salewa Zebru Responsive Long-sleeve Top £80 (UK)170g / 6ozAlpine wool (83%) and manmade polyHiking, biking, trail running, climbing, alpine adventures
Arc’teryx Rho Hybrid Half Zip Baselayer$125 (US)/ £95 (UK)170g / 6ozMain fabric: Phasic AR II (100% polyester with DAO finish), Zoned panels: Nucliex 150 (87% Wool, 13% Nylon, RWS wool)Winter hiking in the hills and peaks
Helly Hansen Lifa Merino Mid-weight Hoodie $120 (US) / £90 (UK)330g/11.6ozMerino wool and Lifa (polypropylene yarn)Winter hill hiking, skiing and alpine adventures
Smartwool Women’s Merino Sport Long Sleeve top$90 (US) / £85 (UK)Women’s: 110g / 3.88oz; Men’s: 138g / 4.86ozMerino wool (53%), Tencel Lyocell (47%)Hiking, backpacking, mountaineering, trail running, snow sports and yoga
Rab Forge Long-sleeve Tee £50 (UK)178g/6.3ozMerino wool (47%) and polyester (53%)Hiking, biking, trail running, climbing, alpine adventures
Paramo Grid Technic base layer £75 (UK) / €100 (EU)238g/8.4ozParameta G (polyester)Hiking, biking, trail running, climbing, alpine adventures
Saxx Roast Master Mid-Weight Long Sleeve$75 (US) / £65 (UK)Men’s large: 221g / 8ozRecycled polyester (87%), Tencel lyocell (9%) and elastane (4%)Hiking, trekking, backpacking, mountaineering, trail running, snow sports and camping
Columbia Omni-Heat 3D Knit Crew II base layer shirt $85 (US) / £70 (UK)232g/8.2ozPolyester (85%) and elastane (15%)Skiing, snow-boarding, alpine adventures and cold-weather hiking, biking and trail running
Craghoppers First Layer Long-Sleeved T-Shirt £35 (UK)230g / 8.1ozRecycled polyester (77%) and viscose (23%)Hiking, biking, trail running, climbing, alpine adventures

How we test base layers

Our reviewers test base layers in a range of environments and conditions, from wintry hills and peaks to warm hikes along the coast, mixing day hikes and longer expeditions. Features (including breathability, odor-resistance, ventilation, materials, style, weight and overall comfort) are tested against claims made by the brand, and we assess factors such as value for money, durability, functionality and environmental impact.

Meet the testers

Pat Kinsella modelling a base layer in Wales
Pat Kinsella

Writer, editor and enthusiast of anything involving boots, bikes, boats, beers and bruises, Pat has spent 20 years pursuing adventure stories. En route he’s canoed Canada’s Yukon River, climbed Mont Blanc and Kilimanjaro, skied and mountain biked through the Norwegian Alps, run an ultra across the roof of Mauritius, and set short-lived records for trail-running Australia’s highest peaks and New Zealand’s Great Walks. He’s authored walking guides to Devon and Dorset, and once wrote a whole book about Toilets for Lonely Planet. Follow Pat’s escapades here.

Julia Clarke  modelling a base layer in Wales
Julia Clarke

Julia is an author, mountain enthusiast and yoga teacher who loves heading uphill on foot, ski, bike and belay. She recently returned to her hometown of Glasgow, Scotland after 20 years living in the USA, 11 of which were spent in the rocky mountains of Vail, Colorado where she owned a boutique yoga studio and explored the west's famous peaks and rivers. She is a champion for enjoying the outdoors sustainably as well as maintaining balance through rest and meditation, which she explores in her book Restorative Yoga for Beginners, a beginner's path to healing with deep relaxation. She enjoys writing about the outdoors, yoga, wellness and travel.

best hiking backpacks: Jessie Leong
Jessie Leong

A former brand ambassador for Merrell and current Ordnance Survey #GetOutside Champion, Jessie Leong’s lifelong outdoor odyssey began with Duke of Edinburgh’s Award walks in the Peak District. This segued into long hill hikes in the Yorkshire Dales, multi-day treks in the Lake District, scrambles in North Wales and adventures scaling alpine pinnacles. When not walking, she can be found rock climbing, wild swimming, cycling, photographing, filmmaking, writing and modelling. Jessie’s most recent claim to fame is playing a Miss World contestant in the 2020 feature film Misbehaviour.

best hiking boots: Matthew Jones
Matthew Jones

An outdoors writer and editor, Matt Jones has been testing kit in the field for nearly a decade. Having worked for both the Ramblers and the Scouts, he knows one or two things about walking and camping, and loves all things adventure, particularly long-distance backpacking, wild camping and climbing mountains – especially in Wales. He’s based in Snowdonia and last year thru-hiked the Cambrian Way, which runs for 298 miles from Cardiff to Conwy, with a total ascent of 73,700 feet – that’s nearly 2½ times the height of Everest. Follow Matt on Instagram and Twitter.

Emily Woodhouse
Emily Woodhouse

An adventure writer based on Dartmoor, England, Emily is an active member of Mountain Rescue and a summer Mountain Leader, but loves all things adventure – before her third birthday she had lived on three continents. Founder of Intrepid magazine, she works to help break stereotypes about women in the outdoors. Her expeditions have included walking all Dartmoor’s 119 tors in a single two-week outing, cycling to Switzerland and back, and riding the Rhine from source to sea.

How to choose the best base layer

best base layer: Matt Jones in base layer

Next-to-skin comfort is very important in a base layer (Image credit: Matthew Jones)

While there are myriad styles to choose from, the best base layers are there to do one job well: keep the wearer warm and safe. Additional features will add comfort and functionality, but the thermal properties are the most important factor. The following are some things to consider.

Thermal insulation

The best base layers work by trapping air, which is then warmed up by your body heat to provide a thermal layer. For this to work well, the garment must be made from a material that holds on to air well, but gets rid of water quickly.

Materials

Natural fabrics – especially merino wool, but also bamboo – work very well in the best base layers, but you’ll often see manmade materials like polyester and Lycra employed in the mix, and these can help make the garment closefitting (as a base layer should be), maintain its shape, add to its durability and improve the all-important thermal performance, especially if it gets wet. 

Merino wool is a magic material that keeps you warm when you need it to, but can also cool you down when outside conditions are hot. It also wicks moisture away from your body, feels comfortable and boasts antibacterial properties, which stop tops from getting too smelly. Garments with a high percentage of cotton should be avoided, as cotton holds onto water and performs terribly when wet, losing all its thermal properties and keeping you cold.

Comfort

Next-to-skin comfort is very important in a base layer, for obvious reasons. Most people find merino wool extremely comfy, but others prefer bamboo, or synthetics such as brushed fleece. This is subjective, but worth getting right, otherwise you’ll spend all your time itching. Tops with flat-lock seams will be more comfortable to wear.

Fit

Ideally, the best base layers need to hug you tight. You don’t want the back of the sleeves riding up to expose bare skin to the cold, and a top that wrinkles under another layer won’t be comfortable.

Features

Lightweight base layers are less likely to have them, but in a more substantial base layer, a partial-length zips is an excellent feature, allowing you to dump excess heat during activities. We like thumb loops too, which stop sleeves from riding up when you put on another layer, and prevent gaps appearing between your top and your gloves.

Moisture management

While outer layers have to cope with mist, rain and snow, base layers must deal with sweat, so they need to be breathable and have the ability to wick moisture away from your body.

best base layer: Emily in Artilect

Base layers need to be breathable and have the ability to wick moisture away from your body (Image credit: Emily Woodhouse)

Weight

Base layers are often ascribed a weight (for example, ‘midweight’), which relates to the thickness of the piece of clothing in question. Obviously, the higher the weighting, the warmer the garment will be. It’s definitely possible to have a base layer that’s too hot, so go with an option that best suits the type of outdoor activity you do most often, in the kind of conditions you’re most likely to be out doing it in.

Durability

While merino wool is one of the best base layer materials, it does only last so long and it can lose its shape, which is why many brands use a mix of wool and hardier synthetic fabrics.

Environmental concerns

As always, the most sustainable clothes are the ones you’ve already got, but if you do need to invest in a new base layer, look for garments woven from natural, biodegradable materials (wool, bamboo) or recycled synthetics, made with natural dyes by brands with good environmental principles and robust manufacturing ethics.

Our guide to the most eco-friendly outdoor brands will point you in the right direction.