One of the best base layers forms the foundation of any outdoor getup. Especially when the weather is cold, using a layering system with your outfit is the only way to ensure you stay warm and dry, but can also cool down when you need to. The base layer, as you might have guessed, is the first of many thin layers designed to be added or removed at will, to ensure you stay a comfortable temperature, whatever activity you're embarking on and whatever the weather is doing. If you're hiking, for example, you might add a fleece jacket and one of the best waterproof jackets on top.
They're typically comfortable, stretchy and close fitting, to make layering up easy, without excess fabric getting twisted or adding bulk. The best base layers achieve a clever trick of wicking away sweat when you get active as well as providing you insulating warmth in cold conditions. Jump to the bottom for some more buying advice (including what the best fabric for a base layer is), or read on for our ranking of the best base layers to buy now. And if you're heading to the slopes, we have a separate guide to the best ski base layers.
The best base layer 2021
You know all about Merino wool, of course you do, but you should also know that most base layers and T-shirts that claim to use it do so only sparingly. Icebreaker's Tech Lite is virtually all merino, which makes a big difference. As a base layer it's soft, warm and wicks away moisture really well, and at 146g it's in Icebreaker's ‘150 Ultralight' range. A capsule-wardrobe classic, the Tech Lite is a classic among frequent travellers and 'flashpackers' because it works great as a regular T-shirt (it's not as figure-hugging as most base layers) that's very odour-resistant even in humidity, and can be wrung-out in a sink and dried in hours. Whisper it, but you can wear an Icebreaker Tech Lite for days on end without getting wiffy. The only drawback is that Merino does lack longevity, which is why most brands don't get much beyond 50%; expect it to thin-out and get holes after about a year or two of heavy use (top tip: keep it for hikes and holidays only).
The Le Col Thermal Long Sleeve Base Layer is a good example of why you shouldn't judge a book by its cover. It's not like the Le Col Thermal Long Sleeve Base Layer is ugly; on the contrary, it looks pretty neutral yet – due to the ergonomic outline – well fitted and sleek. The branded collar adds just enough detail to a piece of clothing that otherwise sits under many other layers of tops, jumpers, jackets and the likes. No, what I meant about not judging the Le Col Thermal Long Sleeve Base Layer is because it is in fact 100% synthetic, but it doesn't feel like a synthetic at all. I don't think I ever wore anything that felt as soft as the Le Col base layer, and that includes my beloved satin underwear.
Also, don't let the fact that Le Col is a cycling brand fool you. The Le Col Thermal Long Sleeve Base Layer is equally as good for running, hiking or just walking as it is for cycling, and the Coolmax fabric will wick moisture away from the body effectively, regardless of the type of exercise you do.
When the mercury really drops, we think the best base layer around is the Kora Yushu LS crew. It's made with a combination of yak wool and superfine merino that the brand has dubbed 'Hima-Layer' fabric (pause for applause for that pun). We tested the women's version on out on a very cold day skiing in Austria and were extremely impressed with it. It kept us much cosier than our synthetic base layer managed, but didn't get at all clammy. All seams are double stitched, and high-wear areas use durable corespun merino yarns for durability. It's close-fitting but not skin-tight. If we were to nit-pick, we wish the body was a little longer.
Dress for the bottom of the mountain and you're going to get a cold shock 10 minutes later when a cable car dumps you on the peak. Skiing off the tops of icy, freezing mountains on super-cold days requires careful layering, which is why Helly Hansen make this two-in-one. On the outside is an all-merino wool layer, while next to your skin is a grid-style layer of LIFA Stay Warm Technology fabric. Thankfully the latter is just as softer against the skin as the former. Keeping merino's moisture-wicking properties and adding an extra-warm layer, this is one of Helly Hansen's warmest base layers that's perfect for any type of activity in cold weather. This one comes with flat lock seams for comfort and a 1/2 zip construction for letting-off a bit of steam. This is the ‘lightweight' version; a ‘heavyweight' version is also available for super-cold adventures.
The Finisterre Bora (for men) and Vela (for women) are short sleeved base layers made from a blend of bamboo and organic cotton designed as a vegan-friendly alternative to Merino wool. The fabric is stretchy, soft and super-comfy to wear, as well as being thick enough to don as a T-shirt and worn on its own. That thickness has it's down-sides; the fabric isn't quite as breathable as others we've tried, and will probably be a bit warm to wear in hot weather. However, the Vela and Bora still earn their place in our best base layer guide for delivering a versatile, hardwearing and high quality layer at a competitive price. Head to our Finisterre Vela / Bora Bamboo base layer review to find out more.
All brands have their own technical fibres, but Columbia's Omni-Heat 3D does look a bit… weird. Its thermal technology is now over a decade old and works by reflecting body heat while also wicking away sweat, but its more recent '3D' update sees a new three-pointed star pattern that keeps the heat in. However, that pattern is presented in a very shiny, reflective silver, so it looks like the inside of this base layer – aside from strips of breathable polyester/elastane mix fabric on the flanks and spine – is covered in tin foil. It also has a bit of grip, so it's as odd to wear as it is to look at. Reservations disappear when worn because this base layer's performance is excellent; toasty warm and dry. We loved the optional thumb loops on the sleeves, and after first-wear, we also loved its unique high-tech look.
You might be surprised to hear that Runderwear does other things than just chafe-free underwear for runners – the brand also manufactures chafe-free tri-suits, chafe-free headbands and neck warmers and also, chafe-free base layer tops. And not just any chafe-free base layers, but comfortable ones that actually work well for runners.
I guess this last bit is not surprising, given that Runderwear knows exactly how to create fabrics that feel good on the skin and stitching that doesn't rub against the sensitive areas of your body. The Runderwear Long Sleeve Baselayer Top encompasses all the good qualities Runderwear has to offer, as well as adding some really cool features, like the removable mitts, so you don't have to carry running gloves around.
I tested the Runderwear Long Sleeve Baselayer Top running the Vitality Big Half in early March, the weather still being cold and the running top passed the test with flying colours. It kept me warm in the pit at the beginning and thanks to the moisture wicking and the dynamic heat control technologies, it wasn't too warm later in the race either. The best base layer choice for runners.
A simple classic Merino wool layer for all occasions, the Finisterre Eddy is an understated baselayer champion. Finisterre’s dedication to materials gives you full supply-chain traceability as well as mulesing-free Merino, both best for peace of mind. Long sleeves add warmth in the cooler months, and protection in hotter climes, while the forward-facing shoulder seams increase comfort. Merino is naturally odour-combating, as well as temperature regulating and comfortable next to the skin to boot. Designed in the UK and manufactured in Portugal, the Eddy is a homespun winner. The only thing that might put some people off is the looser fit.
The North Face Men's Sport Long Sleeve Zip Top has a seamless design to reduce unnecessary chafing and discomfort during exercising. The special body mapped ventilation ridges, holes and patterns create an effective moisture management technology that wicks away sweat but keeps your muscles warm. This base layer is fully synthetic which might put some people off, since you won't get the benefits of natural Merino wool yarns. In the same time, the mix of synthetic fabrics used for the The North Face Men's Sport Long Sleeve Zip Top makes it an excellent compression top for people who don't like compression tops.
In a true The North Face fashion, the materials used in the base layer are sourced responsibly; not sure where you'd source synthetic fabrics though? Regardless off this, The North Face Men's Sport Long Sleeve Zip Top will keep you energised fresher for longer, whether you run or hike this winter.
The brand Canterbury might be synonymous with rugby but its products can be used outside the field, too. Thermoreg base layers use specially-designed fabric technology that regulates temperature and wicks moisture to the surface to keep you dry – a feature that comes in handy when hiking or hitting the gym too. An antibacterial finish makes it tough for odour to cling, while the quick drying fabric means this base layer is ready to go faster after a wash. Offset side seams allow full range of movement and the underarm gusset provides additional comfort. Since it was designed for rugby players, the sizing-range is quite generous: it goes from extra small all the way to 4XL, so even people with larger frames can enjoy the benefits of the Canterbury Thermoreg Long Sleeve Base Layer.
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What's the best material for base layers?
There are many (many) ingenious hybrid fabrics used in base layers, from carbon fibre to silver, but they can broadly be split into two camps: those made from merino wool and those created using synthetic fibres.
The famous (and expensive) merino wool is warmer by weight, more comfortable and absorbs less body odour. Merino wool retains heat, it's breathable so it allows sweat to escape, and as a bonus, it's naturally antibacterial so can be worn for days on end without needing to be washed. For general travel, it's unbeatable. However, it doesn't last long.
Though there are many hybrids that use a mix of both, the other end of the spectrum is the wholly synthetic base layer. They tend to use various polyester blends that are also breathable, but perhaps not quite as warm as merino. Artificial materials tend to be hard-wearing and easier to engineer and body map. That means they're generally lighter and longer-lasting.
What else should I look for in the best base layer?
Something else to think about when looking for the best base layer for you is ventilation and how it's designed-in. Although you're preparing for the cold, if you're likely to sweat (i.e. you're exercising), it's very likely that even the finest merino wool won't be able to wick away every last bead of sweat. So whatever the material it's made from, a base layer that can be unzipped at the front can allow you to cool down quickly with a burst of cold air. Simple, but effective.