No matter how you prefer to enjoy the outdoors, base layers can help keep you comfortable out there. Choose them wisely, and you’ll stay warm and dry whether you’re cross-country skiing, winter camping, or spending a day on the slopes. Choose poorly, and you might be drenched in sweat or shivering (or both!), no matter what else you’re wearing. Base-layer tops can be worn alone or under a shell or insulated jacket, while bottoms are almost always meant to go under soft-shell or hard-shell winter pants (though some can double as standalone leggings). 

Base layers come in a variety of different materials and weights, each best suited to a particular type of winter recreation. Here’s how to choose the best base layers for all your activities.

In this article, you’ll learn:

• The pros and cons of different base layer materials
• How to choose the best base layer thickness
• Other base layer features to consider 

BASE LAYERS FAQs

What is moisture-wicking fabric?

Fabrics that are made from wicking materials are designed to take moisture from your body and pass it through their fibers, spreading that moisture out over a larger surface area farther away from your skin. This means you won't get soggy because the fabric can dry faster and stay dry longer.

How many base layers do I need? 

Body temperature determines how effective your base layers are, so adjust your base layers based on your level of activity and keep in mind how quickly you tend to get sweaty.

One more tip: You should try to keep your bottom half just as warm as your top half, so use this guide to help achieve full-body comfort.

What are base layers for?

Weather is a huge factor here. You can still sweat even in colder climates, so this is where base layers are key. Lower temperatures can make your regular sweat turn to cold sweat if it doesn't get properly pulled away from your skin, making an already uncomfortable feeling potentially dangerous. Not properly insulating or cooling your body can lead to medical problems like hypothermia, heat stroke or frostbite. 

Are base layers the same as thermals?

The short answer: no. Thermals aren't made to fully wick away moisture like a standard base layer, but they are intended to help keep you warm. Base layers aren't necessarily meant to keep you warm, but instead to help keep you dry and properly insulated. Thermals and base layers should not be used interchangeably, because their intended functions are different. Thermal = warm. Base layer = not cold.

BASE LAYER MATERIALS
 

Generally, base layer materials can be sorted into two camps: natural materials (primarily merino wool, but also plant-based rayon and hemp) and synthetic materials (polyester, nylon, spandex). 

To help you get an idea of what’s out there, we’ll start with the actual materials that base layers are made from. Some are better than others depending on your level of activity, but first, let’s get a base layer of understanding on the options you have to choose from.

Wool Base Layers & Other Natural Materials

Let’s get one thing straight: Today’s wool is not itchy. Made from ultrafine fibers sourced from Merino sheep, merino wool is soft and comfortable against the skin, never abrasive. And some of the plant-based natural materials, like bamboo-derived rayon or wood-based lyocell or modal, feel even cushier. Other reasons to love these fabrics: They are breathable and great at moisture management, wicking sweat away quickly. Though wool retains moisture within its fibers, it still feels dry against the skin. Plus, merino wool is naturally antimicrobial, preventing the growth of odor-causing bacteria for an impressively long time. 

On the downside, merino wool is not as durable as synthetic fabrics and often pills with abrasion (like under pack straps). It is slow to fully dry and tends to be the most expensive option. 

Worth noting: Some wool production has been associated with mistreatment of the sheep that grow it. In response, some brands have developed standards for their suppliers to ensure the humane treatment of sheep and systems to trace their wool back to the ranches for accountability.

Synthetic Base Layers

Typical synthetic fabric is made from polyester or nylon, often with a bit of spandex added for stretch. These fibers excel at wicking and drying quickly. They’re more durable than natural fibers and usually cost less. But! They’re notorious for getting stinky fast (some have anti-odor treatments, which can help). Synthetic fabrics are also derived from petroleum, but more brands are using recycled fibers to reduce the environmental impact of their layers.

Blends & Combinations

Some base layers use both natural and synthetic fibers to take advantage of the best qualities of each. One common construction sandwiches a synthetic layer to a wool layer—one on the inside, one on the outside—to deliver fast wicking with odor control. Another wraps a wool fiber around a nylon core for added durability.

Silk Base Layers

Silk is less frequently used than wool or synthetic materials, but it has some solid benefits. It’s super soft, which is great for sensitive skin. It wicks moisture well and is lightweight and thin, but it may require more washing. If you’re wearing tight clothing, silk is a great option for underneath because it likely won’t be as visible as other thicker fabrics.

Bamboo Base Layers

Bamboo as a base layer is a fairly new option and not super common, but it’s worth mentioning. Fabric from bamboo is made with bamboo extracts blended with other fabrics to enhance the fit and soften rougher materials (like wool). It is also antibacterial and moisture wicking, and tends to be friendly to sensitive skin.
Pro Tip: Stay away from cotton. It’s not great at getting rid of moisture, and there are plenty of other options designed for durability, comfort and warmth.  

BASE LAYER WEIGHT

Another major factor in base-layer shopping is the garment’s thickness, or weight. This plays an important role in how warm the base layer is. Not surprisingly, thicker fabrics tend to be warmer than thinner ones, but your level of exertion matters a lot in this equation. Also consider if you usually run hot or cold; the perfect layer for one person at 20°F may be way too warm for another. Base layers are typically classified in these three categories:

Lightweight

Thin and light, these base layers are ideal for warmer weather (making them great for three-season use) and/or high-exertion aerobic activity. Think skating, skiing or trail running. Lightweight base layers work well on their own, and they dry faster than thicker options.

Midweight

Medium-thickness base layers excel for moderate activities in cool weather—like resort skiing or hiking—or more aerobic activities in colder temps. 

Heavyweight/Expedition Weight

The plushest, heaviest base layers are made for exceptionally cold weather and more moderate activities (like winter camping). They are usually too hot for highly active wear.
 

BASE LAYER FEATURES

Base layers tend to be fairly simple in design, but there are a few useful features to look out for:

Zippers

Some tops include a quarter- or half-length zipper from the neck down, making the layer more versatile. Zip it up to your chin in colder weather or unzip it when you start to heat up.

Thumbholes

These holes let you pull a shirt’s sleeves halfway over your hands, adding warmth. Make sure to check the fit: Too-tight thumbholes are uncomfortable to wear.

Hood

Close-fitting base layer hoods add a significant amount of warmth, as well as sun protection. 

Pockets

Some base layer tops and bottoms feature zipper pockets on the shoulder, forearm or backside. These can be handy for storing keys or IDs but remember that they will only be accessible if you are wearing the layer on its own. 

Boot cut

Skiers love this calf-length design for base layer bottoms because it won’t bunch up uncomfortably under ski or snowboard boots.

High waist

Bottoms that come up to the belly button or higher fit comfortably under hip belts and harnesses.

BEST BASE LAYERS BY ACTIVITY

Running: Base layers for running are important, and you’ll want to pay attention to the weather first and foremost. Be sure to wear a lightweight layer if it is cool outside or opt for midweight when the temperature starts to drop. Base layers with thumb holes are also smart because they will help prevent the sleeves from shifting up as you pump your arms. Synthetic materials are great for running because they are lightweight, breathable and wick moisture efficiently, but pick the fabric that is most comfortable for you to maintain consistent activity.

Hiking: This is a pretty low-exertion activity, so you’ll want to use the temperature outside as a gauge for how to dress. Is it colder? Bundle up. Warmer? You may want to go with a lightweight base layer. Material is not a huge factor here, so focus on comfort and make sure you give yourself the option to shed layers if necessary. 

Backpacking: Though you may be on the same path as when you hike, the big difference here will be your pack. More weight = more physical exertion. Try out a lightweight or midweight layer that allows for airflow (like merino wool) but dries quickly (like synthetic). You’ll likely be out in the elements for longer periods of time, so make sure you have more than just a base layer to keep you warm.

Climbing: You’ll need to make sure your muscles are well taken care of while you’re out in the elements. Look for something with a looser fit that’s on the thicker side because your muscles need more room to flex as much as they need to stay warm and dry. Learn more in our Rock Climbing Base Layers Buying Guide.

Biking: Whether you ride your bike to work or rip along wooded trails on the weekends, you’ll need to protect your skin from the elements and keep your body temperature from spiking. A lightweight base layer is a great all-around option to start with, because it’s easy to get subtly sweaty as you ride and you want to consistently wick moisture and regulate your body temp. You can add layers as needed to protect against wind and other potential damages.

Snowsports: Activities in the snow present probably the most obvious need for a base layer. Start with a lightweight layer that focuses on wicking moisture to get the initial sweat out the way, then add on a midweight or heavyweight layer to keep you extra warm. You may get hot as you move and can shed layers as needed, but you should have at least one base layer to start. 

FINALLY, THE FIT

The most important thing to remember about a base layer is that it’s there to wick away moisture and regulate your body temperature. To do that properly, you need to have a tight fit. If your base layer isn’t flush against your skin, the fabric won’t have the ability to redistribute your sweat to keep you dry. 

READY TO FIND THE RIGHT BASE LAYER FOR YOUR NEXT ADVENTURE? START HERE.

All articles are for general informational purposes.  Each individual’s needs, preferences, goals and abilities may vary.  Be sure to obtain all appropriate training, expert supervision and/or medical advice before engaging in strenuous or potentially hazardous activity.