Now, you may be asking yourself, “Why do I even need a base layer? I have enough stuff to keep me going in any temperature and I'm tired of money grabs. Why should I bother buying something that I can just substitute with a long-sleeve shirt or an extra zip-up?”
First of all, why are you so angry? Second of all, while those are all valid points, there's a little more behind base layers than them just being another thing to buy. The whole point of wearing a base layer is to keep your body temperature from spiking all over the place while you're active and to keep you dry when you start sweating. That way you're not gross, smelly and uncomfortable, and you can stay active longer.
The term “moisture-wicking” is something that's going to come up a lot, so you should probably know what it means. It's pretty integral to everything base layers are about. Fabrics that are made from wicking materials 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. What this means for you is that you won't get soggy, because the fabric can dry faster and stay dry longer.
Another thing to remember is that nobody knows your body as well as you do. Body temperature determines how effective your base layers are, and just because your sweet cousin Jimbo runs cold doesn't mean you do. Adjust your base layers based off your level of activity and keep in mind how quickly you tend to get sweaty.
Weather is a huge factor as well. You'll still sweat even if you're in colder climates, so it's important to make sure you don't feel the need to start ripping off layers in the snow to give yourself some temperature relief. Lower temps 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 that make you say “Yikes,” like hypothermia, heat stroke, or frostbite. You could also get sick, and no one likes a sneezer.
Also, there's an important distinction when it comes to base layers vs. thermals that I want to clear up before we start. Thermals aren't made to fully wick away moisture like a standard base layer does, but are intended to keep you warm. Base layers aren't meant to keep you warm, but instead to keep you dry and properly insulated with the assistance of more layers. Thermals and base layers cannot be used interchangeably, because their intended uses are completely different. Still with me? Thermal = warm. Base layer = not cold.
One last thing: I'm not just talking about a base layer shirt here. You should try to keep your bottom half just as warm as your top half, so use this guide as a stepping stone for full-body comfort.
To help you get an idea of what’s out there, I’m going to 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 what options you have to choose from.
• Synthetic: This is one of the more common types, and it usually means the material is some sort of polyester or polyester blend. It dries super fast and is usually lightweight, so it’s not designed for obscenely cold weather. Think instead: a cold winter day. Try to avoid the arctic. It’s a little more versatile for warmer weather as well, so you have a wide range of use. It’s also pretty durable and usually inexpensive. It’s not overly antibacterial, so make sure you give it a good wash with specialty cleaner more frequently than not.
• Merino Wool: The other more common type, a merino wool base layer is made of a gentler type of wool that’s less irritating to the skin. It excels at regulating body temperature, so it’s great for insanely cold weather but won’t have you overheating when things start warming up. It’s relatively durable, but is susceptible to wear and tear the more you use it or if you store/wash it improperly. It’s naturally moisture wicking, but can be slower to dry in some cases.
• Silk: This material is way less frequently used than wool or synthetic materials, but it has some pretty solid benefits. It’s super soft, like...uh...silk, so those of you with easily irritated skin may like how it feels. It wicks moisture pretty well, and is very lightweight and thin, but it’s also not great at keeping the stink away, so it requires 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: This one is fairly new, and not super common, but it’s worth mentioning. Fabric from bamboo is made with bamboo extracts and is blended with other fabrics to enhance the fit and soften up rougher materials (like wool). It has a lot of features seen in other base layers, like how it’s antibacterial and moisture wicking, but it tends to be a little more friendly to sensitive skin.
Pro Tip: Stay away from cotton. It really sucks at getting rid of moisture, so you’ll be soaking wet for longer than you can handle. It’s warm, yes, but there are other materials that are warm that you can choose from. Just don’t do it, okay?
This is pretty straightforward, but we need to go through it anyway. Sorry.
• Lightweight: On the thinner side, lightweight base layers are handy because they dry quickly with less of a fight. They’re not built for maximum insulation, but they’re great for less vigorous activities or when you know you’ll be working up a wicked sweat. Keep these on hand for more moderate days or when it gets cooler, or if you’re a naturally hot person.
• Midweight: A handy middle ground, these are slightly thicker so you can use them as a base or second layer, depending on the weather. They’re best for colder temps and balance moisture wicking with insulation pretty well.
• Heavyweight: These are made from thicker fabrics and aren’t always something you should be wearing as a first layer. Each situation is unique, of course, but heavyweight base layers can be more focused on keeping you warm rather than keeping you dry. That being said, they’re the best layer for cold weather because they can provide that extra boost of insulation.
The Takeaway: Make sure you focus on moisture wicking ability when it comes to base layers that are closest to your body. While monitoring your body temperature is insanely important, the thing you should pay most attention to is keeping yourself dry.
I know there’s about a million activities you can do that make you sweat, so we’re gonna go back to basics and give you the best starting point to help you choose for more specific activities when it comes time to do so.
• Running: Base layers for running are pretty important, and you’re going to want to pay attention to the weather first and foremost. Be sure to wear a lightweight layer if it’s only cool outside or go midweight when the temperature starts to drop. Base layers with thumb holes are also smart, because it prevents the sleeves from shifting up as you pump your arms. Synthetic materials are great for running because they’re lightweight, breathable, and wick moisture really efficiently, but pick whatever is most comfortable for you since you’ll be doing some pretty consistent activity.
• Hiking: This is a pretty low-exertion activity, so you’re going to need to use the temperature outside as a gauge for how to dress. Is it colder? Bundle up, baby. Warmer? Maybe go for a lightweight base layer. Material isn’t a huge factor here, so focus on comfort and make sure you give yourself some ability to shed layers if there’s a really sneaky, steep hill somewhere along your route.
• Backpacking: Though you may be on the same path as when you hike, backpacking’s core difference is the stuff you’ll be lugging around. More weight = more physical exertion. Try out a lightweight or midweight layer that allows for airflow (like merino wool) but dries quickly (like synthetic). Your back is gonna be sweaty regardless. Just accept that now. Alongside that, you’ll probably 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: This is the kind of activity where you’re probably like, “What?! I don’t need a base layer for that!” And you’re definitely wrong. You’re out in the elements and you need to make sure your muscles are well taken care of. 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.
• 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 all over the place. 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, as long as you’re protected against wind and other potential damages.
• Snowsports: Activities in the snow are probably the most obvious need for a base layer. You have to stay warm, so you may need more than one base layer to keep things at the right level of performance. 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 that can keep you extra warm. You’ll get hot as you move and can definitely start to strip down as needed, but you should have a minimum of one base layer on no matter what. Sorry, I don’t make the rules.
The most important thing to remember about a base layer is that it’s there to wick away moisture and regulate your body temperature. In order to do that, you need to have a tight fit. I know it may seem like having a looser item makes it easier for the air to flow, which isn’t entirely untrue, but if it’s not flush against your skin then you take away the fabric’s ability to redistribute your sweat to keep you dry. Dry is good. Dry is your friend.
Now that you have your bottom layers, it’s time to choose a top one. Just like when you choose a base layer, you’ll want to choose the best outer layer for whatever activity you’re doing. There are a million different types, from waterproof shells to insulated winter jackets. Added features, like ventilation zippers, can aid you in staying cool if you tend to run hot. The key is to keep in mind what your body needs most and find that Goldilocks balance of comfortable adventure.