Best Base Layer: Choosing the Right Layers to Keep You Warm

Best Base Layer
Sean Nelson
Written by Sean Nelson

A good base layer is the foundation on which your technical clothing rests. Base layers are designed to sit close to the skin and absorb sweat as you exercise. The sweat can then evaporate away from your body, keeping you warm and dry.

Some base layers look good enough to be worn as outerwear, and this is fine – these are not just cold weather garments. The moisture wicking properties of a good base layer will be beneficial even in warm weather. In cool or very cold weather, your base layer should be the basis for a considered selection of further layers.

A sweater or hoodie on top of your base layer followed by a down jacket will create a warm and versatile armor against the cold. You can choose from two main types of materials when looking for the best base layer, merino wool or synthetic fabrics.

Our top picks

Smartwool PhD NTS Light 195Merino woolCold weatherCheck price on Amazon
Marmot ThermalClime Pro CrewPower dry fabricCold weatherCheck price on Amazon
Rab Merino+ 160 LS CrewMerino wool and polyesterCold weatherCheck price on Amazon
WoolX Everyday ShirtMerino woolWarm weatherCheck price on Amazon
Ibex Woolies 2 Crew ShirtMerino woolCold weatherCheck price on Amazon
Smartwool NTS Mid CrewMerino woolVery cold weatherCheck price on Amazon

Things to consider before buying

Choosing a good base layer can be quite daunting, especially if you’re going in blind. If that’s the case with you, it’s best yourself that you familiarize yourself with a number of essential factors that will allow you to choose a good base layer.

Type of Fabric

Among the most important aspects to keep in mind when selecting what to buy, one of the most important is the type of fabric your layer has. Here you have what we consider are the best.

Merino Wool

Merino wool is prized for its light weight, warmth, and softness, and can often be found in products that are worn close to the skin like socks. This natural fiber traps air and warmth next to the skin in the same way that down products do. This also means merino wool fabric is breathable, and you won’t overheat while active.

Merino Wool Base Layer

Another amazing benefit of merino wool is that it has natural anti microbial properties. The lanolin in wool keeps away the bugs that turn sweat into bad odors. The result is a base layer that will always smell fresh no matter how hard you have exercised in it.

The natural wool fibers of merino are also very flexible. Throw your merino wool base layer into a pack at the start of a trip and it will not be creased when you unpack it later. The pliable nature of the fibers also allows the finished garment to move and stretch with you as you exercise. Afterward, the base layer will retain its original shape.

When wicking moisture away from the body, merino wool is very absorbent, holding up to one third of its weight in moisture before you notice any dampness. The difference in temperature between the warm air next to your skin and the cooler air on the outer side of the garment will then allow this moisture to evaporate.

Merino Wool Base Layer

You might worry that merino wool will be a high maintenance fabric, but this isn’t always the case. Many merino base layers can be machine washed at a low temperature, and some can even be tumble dried on a low heat. It is always best to check on your garment’s label before washing.

Synthetic Fabrics

Synthetic base layers are most often made from polyester or polyester blends. These fabrics tend to be more durable than merino, although they can rarely match merino wool’s warmth.

Where synthetic fabrics do beat merino is the moisture wicking. The technical fabrics developed for today’s active wear are built from different layers, each with a different fiber length. These fibers are designed to grab the moisture from your skin and the next layer will then perform the evaporation stage. Merino wool can’t compare to this approach and won’t wick moisture away as well as synthetic fabrics.

Syntetic Base Layer

Synthetic base layers are often easier to wash than wool, which is a good thing because synthetic base layers can get quite smelly. Fatty sweat deposits can get lodged in the synthetic fibers and are difficult to get out without a specialist cleaning product.

Bamboo Base Layers

Bamboo fabric is a relative newcomer to technical clothing but is becoming common as a base layer fabric. It is more durable than merino wool and is easier to care for. Bamboo is less itchy than wool and has a softer, smoother feel than many synthetics. It also fits very well and will have added elastane for extra stretch.

While merino wool is definitely the winner of the smell free prize, bamboo comes as a close second. This natural material also has some anti microbial properties, which helps reduce odors. Bamboo is also reasonably priced, comparing well with synthetic fabrics, and cheaper than merino wool.

Bamboo Base Layers

Additionally, there are some other aspects that are as important as the previous one. Keep reading to find out what they are.

Seasonal Layering

It can be useful to have a different base layer for each season. For a summer garment you will need to look for wicking properties and breathability, while during winter activities insulation will be a priority. Base layers also come in short and long sleeved varieties, and even all in ones for very cold weather (with hoods included).

You can get an idea of which season each base layer is designed for by checking the fabric weight.

Seasonal Layering

Fabric Weight

Most base layers will have a number somewhere in their name. This refers to the fabric weight, and lets you know the sort of weather the top will perform well in. The higher the number, the heavier the fabric weight.

UPF Rating

UPF rating refers to ‘Ultraviolet Protection Factor’. If a garment is rated for UPF it is guaranteed to keep out a certain percentage of harmful UV rays. For example, a garment rated UPF30+ will block up to 96% of UV radiation.

Any garment that lets less than 2% of UV through will be rated UPF 50+. This is the highest available rating.

Base Layer Upf Rating

Cut and Style

The cut and style of base layer you choose will depend on which activities you will be using it for, and what season you will be using it in.

For summer hikes a short sleeved wicking top may be ideal, or you may prefer a long sleeved design to protect your forearms from the sun. Look out for UPF ratings (explained above) on some labels, if sun protection is high on your list of needs.

In winter, long sleeves will help keep your hands warm. Some base layer tops have extra long cuffs that can cover the hands or even fold over the fingers like mittens. A high collar will keep drafts out, and a three quarter or half zipper will help get the top over your head, while keeping drafts out in use.

Base Layer Style

Base layers are usually designed to be a tight or close fit. A closer fit than a usual top is needed to trap a layer of air next to the skin and to help wicking. Base layers should also be wrinkle free when worn to prevent chafing as other clothing layers move against them.

The fancy seam layouts on base layers are also designed to help prevent discomfort. Seams will be placed in areas that aren’t under much pressure. Seams on shoulders will be on the front and back, for example, rather than directly on top where the weight of a coat and backpack could cause rubbing.

Base Layer

Seams should also be sewn flat for less bulk, and more comfort. This style of seam will also wear less than an ordinary seam design unless it is under a lot of strain.


Today’s base layers (even the merino wool ones) can usually be machine washed. Check the garment label to be sure. Most can be machine washed on a cool or warm temperature, and some can even be tumble dried.

Machine washing after every use is essential with a synthetic base layer to stop the build up of odors. Specialist washing products are available to remove unwanted odors from close fitting synthetic garments. As merino wool doesn’t hold onto odors, you may be able to wear it a couple of times on an expedition without it becoming stale.

Base Layer Washability

Some merino wool base layers may require flat drying, so are not quite as convenient as their quick drying synthetic counterparts.

Which are the warmest base layers available?

Now that you know what to look for when buying base layers, take a look at what we recommend as the warmest ones in the market.

Smartwool PhD NTS Light 195
Smartwool Men's Phd® NTS 250

Special features: Hybrid construction with 100% merino wool, made in USA

Best use: Cold weather active wear

Made in the USA, this base layer offers the breathability, warmth and comfort of merino wool plus the wind blocking abilities of polyester. The top is cleverly designed to put the right fabrics where they will be most effective and has a UPF 35 rating.

The front panel has been made from polyester with a 1 CFM windproof rating, to lessen heat loss from wind chill. The back and sleeves are made from Smartwool 100% merino wool fabric, for increased warmth, moisture wicking and breathability.

The Smartwool Phd NTS Light 195 dries quickly and will stay fresh, due to the odor fighting merino wool. The side panels are sculpted to move seams to where they won’t chafe, and the shaped hem increases coverage of the back. A chin guard keeps the zipper comfortable when fastened, and shaped cuffs help keep the hands covered.

Some users have claimed that the cut is too large and the zipper gets loose over time.


  • Great breathability and warmth
  • UPF 35
  • Windproof

  • Large cut
  • Loose zipper

Related: Another good option for backpacking is the SmartWool Trekking Heavy Crew Socks, which significantly absorbs impact.

Check the price on Amazon

Marmot ThermalClime Pro Crew
Marmot ThermalClime Pro Crew

Special features: Polartec Power Dry fabric

Best use: Active wear in cool climates, climbing, skiing

The Marmot Thermalclime Pro Crew is a synthetic base layer made from Polartec Power Dry fabric. The innovative design of the fabric employs longer polyester fibers to soak up sweat next to the skin and shorter ‘upcycled’ polyester fibers on the outside to help evaporate the moisture, moving 30% more moisture than single component fabrics.

Power Dry fabric is also known for its breathability and warmth (although it can’t beat merino wool). It can also be machine washed and is very quick drying.

This top is an athletic fit, and has added stretch without relying on elastane (which holds on to moisture). Flat locked, sculpted seams eliminate any chance of chaffing, and the tag free neckline adds to the comfort.

With a dipped hem in back to give extra coverage, and generous sleeve length, this base layer will keep you warm all round. People have said, however, that the sleeve cuffs are a bit larger than the wrists size and that air flows through and it might be quite uncomfortable.


  • Dipped hem in back
  • Very quick drying

  • Big sleeve cuffs
  • Air flows trough

Related: We also recommend the Marmot Precip Jacket because it has a waterproof and breathable fabric, which can be helpful when backpacking in rainy seasons.

Check the price on Amazon

Rab Merino+ 160 LS Crew
Rab Merino

Special features: 37.5 technology, merino wool and polyester

Best use: Multi day use in cooler weather

The Rab Merino+ 160 LS Crew is a combination natural and synthetic base layer. The mid weight Merino+ fabric combines 63% superfine merino fibers and 37% polyester to make a garment that is both durable and soft. The wool adds breathability and odor control, while the polyester makes drying super quick.

37.5 technology works as part of this top’s fabric to keep your core body temperature and humidity at optimum levels.

This layer has a slim fit shirt designed to fit underneath other garments. It has a classic look, with a striped weave to the fabric and flat locked seams to the front and back of the sleeves. The crew neck is tag free for comfort.

Some people say that the fabric is a bit itchy and that its quality is not as durable as others from our list. People also say that it is not next to skin, which might be a little bit unpleasant.


  • Great breathability and odor control
  • Quick drying

  • Itchy and not so durable
  • Not really next to skin

Related: We also recommend the Rab Vector Pant since it fits well and is really stylish. The snap waistband closure and the YKK zipped fly are features that are worth considering.

Check the price on Amazon

WoolX Everyday Shirt
WoolX Mens Everyday Shirt

Special features: Itch free guarantee, made of merino wool

Best use: Skiing, snowboarding, everyday wear

The WoolX Everyday Shirt is designed for just that – everyday wear. This base layer has a more generous, looser fit than many of the others and would be great layered under a shirt and sweater for everyday warmth. The itch free guarantee means you can be certain that you’ll love wearing this WoolX base layer.

The 100% merino wool construction offers high breathability and, of course, odor control. There are no awkward washing instructions with this top, simply turn it inside out and put in the washing machine. It can even be tumble dried.

While you can wear this shirt on ordinary days, it is designed with performance in mind, too. The drop tail hem gives extra back coverage and the sleeves feature underarm gussets for maximum freedom of movement when skiing and snowboarding. WoolX recommend that this shirt be worn for warmth through fall and winter.

In cold weather, you should use jacket or a sweater since it is not design for too low temperatures.


  • Itch free guarantee
  • Breathability and odor control

  • Not design for too low temperatures
  • Quite loose in comparison to other layers

Related: We strongly recommend you to buy the Woolx Merino Wool T-Shirt since it is lightweight, is odor proof and is really flexible.

Check the price on Amazon

Ibex Woolies 2 Crew Shirt
Men’s Woolies 2 Crew Shirt

Special features: 100% merino, machine washable, merino wool

Best use: Climbing, skiing, snowboarding

Ibex have designed the Ibex Woolies 2 Crew Shirt to be worn next to the skin. It is made from a 100% merino wool mid weight fabric that will be warm in cold temperatures, and breathable enough to keep you dry during activities like climbing, skiing and snowboarding.

There is a wide range of colors to choose from, including stripes, and all have a classic construction with flat locked seams running along the front and back of the sleeves. This base layer has a close fit and a generous length, so will have no trouble keeping drafts out.

The 18.5 superfine wool fibers offer warmth coupled with the flexibility to move with you and retain its shape. A tag free neck adds to the comfort levels. Offering the breathability and odor resistance of merino products, this top is also great for packing. Being machine washable makes this a practical choice, too.

Some people say that this layer feels scratchy and that the cut is too large, making it quite uncomfortable.


  • Tag free neck
  • Great flexibility

  • Feels scratchy
  • Cut is too large

Related: Additionally, we recommend you to buy the Ibex Merino Wool Aire Jacket because it will keep you warm, it will protect you from the sun and it is machine washable.

Check the price on Amazon

Smartwool NTS Mid Crew
Smartwool NTS Mid Crew

Special features: 100% merino wool

Best use: Skiing, snowboarding, very cold weather

Made from 100% merino Smartwool fabric, this top is a practical choice as it can be machine washed on a cool/warm setting and tumble dryed on low.

The 250 weight fabric ensures that this base layer will keep you warm in even the coldest of weather when used in a layering system. When worn on its own in cool weather you will also benefit from the merino wool’s warmth. The breathability and wicking capabilities of merino will keep you dry and warm even when performing strenuous activities like skiing and climbing.

The best selling Smartwool Nts Mid Crew has flat locked seams for comfort, and is designed with unique shoulder panels to move seams away from the top of the shoulder to other areas less likely to chafe. The trim fit offers a longer body length to keep drafts out, and the tapering sleeves are long enough to keep the whole of the wearer’s arm warm.

Buyers have said that it pills off after washing a couple of times and that it is slightly larger than it says in the tag.


  • Flat locked seams for comfort
  • Warmth and breathability

  • Pilling problems
  • Larger than it looks

Related: The Smartwool Phd Compression Calf Sleeve is also a product that we recommend since you can use it in every season of the year to reduce muscle fatigue. The sleeve is made from 48% Merino wool so you can be sure that it can give you enough warmth and great comfort.

Check the price on Amazon

In Conclusion

A quality base layer is an invaluable addition to your outdoor clothing wardrobe. Different bases for different seasons would be even better. If you can afford the luxury of merino wool, you will love the warmth, breathability and odor control of this fantastic natural fiber.

Woman Hiking in Base Layer

If you need a really hard wearing top then the durability of synthetic base layer will serve you well. For those who value a sustainable, planet friendly product, seeking out a bamboo base layer may be the answer.

A mix of synthetic and wool will offer the best of both worlds. Which will it be for you? Which activities and climates will be putting your gear to the test? Let us know in the comments!


Sean Nelson

Sean Nelson

Sean was backpacking since he was 7. He was born close to the RMNP and his father was a ranger, so life surrounded by mountains and wildlife is a norm for Colorado. He likes to explore, but prefers to stay in USA. In his opinion, there are too many trails and options in US to go abroad.