How To Choose The Right Base Layer (Fit, Sizing & Material)

Choosing the right base layer can mean the difference between an awesome outdoor adventure and an awful misadventure.

As your first layer of clothing, a base layer is your first line of defense in staying dry and warm, ultimately keeping you comfortable and healthy while engaging in any outdoor activity.

In this Guide, you will learn:

  • What is a base layer?
  • Why the right base layer is important.
  • How to choose the right base layer.
  • And much more!

What Is A Base Layer?

A base layer is an article of clothing designed to be worn directly next to your skin to regulate your core body temperature.

While it does provide a layer of insulation, its main function is to manage moisture against your skin to keep you dry and comfortable while being active.

A base layer works by moving moisture, whether caused by your body (perspiration) or from outside elements (precipitation), up and away from your skin, through a layer of fabric, to the outside air where it can evaporate or pass to the next layer.

This process, known as “moisture-wicking”, allows the fabric to dry faster, meaning you stay dry longer and staying dry means staying warm.

However, for this to work efficiently, the fabric should be breathable so it can allow moisture vapor to pass through it easily.

A garment with a tighter knit or weave will be less breathable, trapping the moisture inside. With time, it will leave you feeling clammy and uncomfortable. In cold weather, the repercussions can be more significant which we will explain further in the next section.

Base layers are versatile pieces of clothing that come in a variety of styles, materials and even weight thicknesses that will accommodate the different climates and conditions while being active (or inactive).

Whether its tops, bottoms or a one-piece style, as long as the fabric is made with moisture-wicking properties, it can be considered a base layer. 

Why Is The Right Base Layer Important?

As your next-to-skin layer, the base layer is arguably the most important component when it comes to regulating your core body temperature, especially in cold weather conditions.

If you start with the right base layer, you establish a foundation from which to build upon with more layers, ultimately creating an effective layering system. Get your base layer wrong and all the most expensive technical apparel on the market won't help you stay dry, warm and ultimately safe.

Let me explain . . .

Whether you’re active, overly-dressed or just in a warm environment, your body will generate heat and perspire (sweat). Sweating is your body’s natural way of cooling itself off when it gets too hot.

As sweat evaporates from your skin, it takes heat with it, thus cooling you down. This cooling process is known as “evaporative cooling” which helps keep your core body temperature in a healthy range.

However, you don’t just lose heat through sweating. Rain, mist, snow or any other forms of liquid will have the same effect as sweating.

In cold weather, if you allow moisture to remain on or in your clothes, it will begin to cool your core temperature at a time when you slow down or stop to take a break, losing much needed heat. Left damp, this could lead to various cold injuries with hypothermia being the most serious.

Conversely, in warm or hot climates, a damp base layer can be especially uncomfortable.  Since there is a higher coefficient of friction on wet fabrics, it can cause repetitive rubbing and skin chafing that can lead to blisters and sores. If not properly treated or ignored, it can leave the body exposed to further infection.

In addition to managing moisture, in warmer conditions, the right base layer can also help to keep you cool and if exposed, protect you from UV rays.

Basically, when your thermal balance is lost, you will experience thermal discomfort; either freezing in cold weather or sweating in warm weather.  

However, with the right base layer, it can help control your core body temperature so you can keep moving no matter what you’re doing - comfortably and healthy.

How to Choose The Right Base Layer.

Choosing a base layer doesn’t have to be a struggle. If you stay focused on your individual needs, your choice will be that much easier.

To help you choose your best option, we break down the main factors to be considered.

In addition to the above factors, keep in mind that your base layer should match the potential change in weather conditions, temperature, body type and your level of activity.

Now let's get moving!

Base Layer Fit

A base layer’s job is to manage moisture on your skin. As a protective layer for your skin, a good base layer should fit tight to your body. This will help trap heat your body generates, thus elevating your comfort level.

Although you want your base layer to be close-fitting, if it's too tight, it can form hot pockets rather than distribute the warmth evenly, causing you to feel especially uncomfortable.

It’s also important that your base layer doesn’t restrict your range of motion. Your base layer should hug your body like a ‘second skin’, without feeling any sort of pressure from it. 

FIT TIP: Depending on your activity level or for warmer temperatures, opt for a more loose-fitting base layer for increased airflow.

Base Layer Sizing

Base Layer Tops - Your base layer top should cover all exposed areas and have the ability to be tucked into your outer layers while still feeling snug. This will also help keep the cold from getting in.

Base layers fit tighter by design, so it’s best to buy your usual T-shirt size. Don’t be tempted to size down to get a tight fit.

Base Layer Bottoms - Just like base layer tops, your base layer bottoms will also be close-fitting as this will offer more warmth. They should fit right to the bottom of your lower leg and rest around your ankle unless it is a three-quarter length style.

Choose your usual underwear size as this will be adequate when sizing base layer bottoms.

Remember, a base layer can only function effectively if it fits you properly. 

Base Layer Materials

As we mentioned above, not all base layers are created equal. They come in various materials and weights, each working in different ways to keep your core body temperature at an optimal level while being active.

Since base layers are your next-to-skin layer of clothing, the material should be soft and comfortable but also durable. It should be able to withstand the various weather elements, including the activities you put it through, be it a hike, hitting the slopes or simply for daily use.

And because they are in direct contact with your skin, it is extremely important that the material have both wicking and breathability capabilities. 

MATERIAL TIP:  Look for base layers that have flat seams with no labels or tags since this can cause irritation or discomfort.

Generally speaking, Merino wool and synthetics are the most commonly used materials for base layers. The least material used is cotton and for good reason.

Although we love the way cotton feels against our skin, as a base layer, it will do more harm than good. Have you ever heard the old adage, “cotton kills”? Though seemingly dramatic, there is some truth to it.

Cotton greatly increases your risk for hypothermia and other cold injuries since it significantly absorbs more water than any other material. Once wet, it stays wet thereby losing its ability to keep you insulated. So save cotton for those summer days when you’re looking for an extra bit of moisture to help keep you cool.

In addition to Merino wool and synthetics, there are some other materials made for base layer clothing, including silk and bamboo.

Although bamboo is a relatively new type, we thought it was worth mentioning since it can be an alternative for people with sensitive skin.

Let’s examine what each has to offer.


Harvested from Merino sheep, Merino wool is known for providing exceptional warmth, even when wet.

Its natural, ultra-fine fibers are super soft and much gentler on the skin, great for people who tend to be more sensitive.

Wool fibers have impressive moisture-management properties. The cortex of a wool's fiber is "hydrophilic" (i.e., moisture-loving) while the exterior of the wool fiber is "hydrophobic" (i.e., moisture-hating).  As the wool fibers absorb the water molecules, it pulls the moisture away from your skin before releasing it to the outside of the garment where it evaporates.

Not only can wool wick moisture away effectively, it can also move water vapor before it even becomes sweat.

Wool can absorb up to 35% of its weight in water without feeling wet to the touch. The only 2 drawbacks - it takes longer to dry and in warmer weather, a wool garment may feel slightly heavier.

Merino wool excels at regulating body temperature. Not only does it trap air for heat insulation in the bitter cold, but it's breathable fibers allow excess heat to escape from your body, preventing you from overheating. 

Merino wool is also known for its resilience and durability. Wool fibers are not straight but rather have undulations known as crimps. These crimps are what give them its elasticity. Like a coiled spring, once stretched, it’s able to return back to its original natural form by the fibers’ contraction.

Each fiber is also composed of keratin, the same tough fibrous protein found in our hair, nails and outer layer of skin. Incredibly, each wool’s fiber can be bent up to 20,000 times before enduring any damage.

You can even increase durability by choosing a base layer that blends wool and synthetics together.

Honorable Mention: While Merino wool is generally quite durable, as expected with natural fibers, Merino wool base layers may slightly lose its shape through consistent wear and washes. To ensure its longevity, special care will be required when washing. Also, a wool base layer is more prone to surface scarring when worn as an outer layer during any sort of abrasive activity.

Naturally UV-resistant, antibacterial and antimicrobial, Merino wool will protect you from the harsh rays of the sun while also keeping harmful bacteria, mold and mildew at bay, leaving you feeling fresh and odor-free.

Did I mention Merino wool is also static-, flame-, wrinkle-, and stain-resistant?

And if you’re eco-conscious, Merino wool is a naturally biodegradable and renewable resource.

Although Merino wool may not be the most budget-friendly option, it surely delivers on performance which is why it's such a preferred choice.


  • Warmer than synthetics, even when wet
  • Made from natural fibers
  • Soft and gentle on skin
  • Effective moisture management
  • Excels at temperature regulation
  • Durable
  • Elastic
  • Breathable
  • Naturally UV-resistant, antibacterial and antimicrobial
  • Static-, flame-, wrinkle- and stain-resistant
  • Naturally Biodegradable 


  • Slow-drying
  • Can feel slightly heavier when wet in warmer weather
  • Shrinkage is possible if not properly washed
  • More expensive than other materials 


As one of the more common types, synthetics are usually made of polyester or polypropylene, both of which are polymers derived from petroleum byproducts (including recycled plastics).

You might also see nylon, rayon, spandex and polyester blends. Being man-made, they are generally the cheapest of the base layer materials.

Synthetics are lightweight, quick-drying and provide exceptional moisture-wicking, making them perfect for high-output activities and sports.

Synthetics are quite durable; they are able to endure more use and washing, better than most natural fibers.

However, there are some drawbacks. Given that they are man-made, they are not naturally antibacterial which means odor from your sweat will be retained, making them rather stinky unless washed promptly.

Although synthetics run lighter than Merino wool on average, they aren't as warm per ounce, which makes them better suited for more milder climates.

All-in-all, for a cost-effective alternative, a synthetic surely will not disappoint.


  • Lightweight
  • Comfortable on skin
  • Quick-drying
  • Exceptional moisture-wicking
  • Elastic
  • Durable
  • Relatively cheaper than most materials


  • Petroleum based fiber
  • Not naturally antibacterial (unless treated)
  • Not as warm as Merino wool


Although not quite as popular as some other materials, many favor silk for its incredible softness and luxurious feel. For those of you with easily irritated skin, this may be a great option for you.

Although silk can hold its own on its moisture-wicking performance pretty well, it just can’t keep up with other materials like Merino wool and polyester.

Some silk fabrics are even treated to help boost their wicking properties.

As thin and lightweight it is in design, it really packs in an impressive amount of warmth which is why it's ideal for colder weather conditions.

Similar to Merino wool, silk can absorb up to 30% of its own weight in moisture and still remain dry.

But silk does more than just keep us warm in the winter, it can also cool us in the summer thanks to its natural breathable fibers.

Its smooth and weightless material is also perfect to wear under other layers making it less visible than some other thicker fabrics.


In 1897, Rev. Casimir Zeglen, a young priest in Chicago, invented the first bulletproof vest which was made of silk.

Silk does have its flaws though. First, it tends to retain odor more so than any other material requiring more washing which can potentially cause shrinkage.

As a poor conductor of electricity, silk is more susceptible to static cling.

It’s also not as durable as synthetics being more susceptible to UV rays and abrasion which is why it's best to wear silk under a mid or outer layer. And since silk is made from natural fibers, it can be quite costly.

While silk does fall short in some areas, it still makes for a good base layer.


  • Incredibly soft and comfortable
  • Ideal for sensitive skin
  • Thin and lightweight
  • Moderate at moisture-wicking
  • Extremely warm for its weight
  • Naturally breathable
  • Excels at temperature regulation
  • Dries fast


  • Not naturally odor-resistant
  • Hand-washing required more often
  • Risk of shrinkage if not properly washed
  • Not as durable as synthetics
  • More susceptible to UV rays and abrasions
  • Susceptible to static cling
  • More expensive than other materials


Since bamboo base layers are a fairly new creation, they are not commonly available.

If you have very sensitive skin and are easily irritated by wool or a wool blend, this material can be a great option for you.

The fabric is made with bamboo extracts and is blended with other materials to help enhance the fit and soften up other rougher materials such as Merino wool.

Not only is bamboo fabric incredibly soft against the skin, it holds its shape better than Merino wool.

Bamboo fabric even has antimicrobial properties that will help keep you odor-free while its moisture-wicking properties will keep you dry.

Due to its structure, bamboo fibers are extremely breathable. A natural bamboo plant is able to keep itself cool in the heat and like its other properties, maintain it in its fabric form.  The cross-section of the fiber is covered with micro-gaps giving the fabric better moisture absorption and ventilation.  As a result, it can keep the wearer cooler in the heat and noticeably warmer in the cold. 

Bamboo fabric is also anti-static so it won’t cling and UV protective, cutting out 98 percent of harmful rays.

The only downside to bamboo is that they are not commonly available and being a natural fiber, can be somewhat pricier.

Whether you’re looking for a vegan option, one that can thermoregulate, or you have skin that’s easily irritated by wool, then consider bamboo.  


  • Ideal for sensitive skin
  • Incredible soft texture
  • Holds shape better than Merino wool
  • Moisture-wicking
  • Naturally antimicrobial
  • Naturally breathable
  • Exceptional temperature regulation
  • Fast-drying
  • Anti-static
  • UV-resistant
  • Vegan-friendly
  • Eco-friendly


  • Not easily available
  • Quality varies between manufacturers
  • A bit pricey

Base Layer Weights

Before choosing a weight, it’s important to consider both your metabolism and level of activity. Not everyone will require the same weight thickness. While your BFF may be the one always complaining she’s cold does not mean you will be experiencing the same.

Base layers typically fall into one of four categories: Ultralightweight, Lightweight, Midweight and Heavyweight. However, you may come across other similar descriptors like "featherweight" and "microweight" which fall on the light end of the fabric spectrum and “expedition weight” falling on the heavier end.

Ultra-Lightweight (Warm to Mildly Cool Temps) - Being the lightest on the fabric spectrum, they are best for warm to mildly cool conditions.

Wear it as a solo piece or as part of your layering system for a bit more warmth. It’s moisture-wicking properties will definitely keep you dry and comfortable while on the go.

Lightweight (Moderately Cool Temps) - A step up from Ultra, these will be slightly heavier. This base layer weight has exceptional moisture-wicking and drying capabilities.

Most outdoor athletes prefer a lighter layer against their skin, even though it provides minimal insulation. To make up for that, a skier or snowboarder may choose to combine layers by wearing a lightweight under a midweight or a heavyweight piece. This will feel snug against the skin which is ideal for moisture-wicking.

While lightweight layers are designed to be part of a layering system, they can also be worn as standalone pieces in mild to cool conditions provided you are engaging in some kind of high-energy activity.

Midweight (Colder temps)
Midweights are the happy medium and considered to be the most versatile.

Typically worn as your next-to-skin layer, it can also serve as a second layer over a lighter base material.

Providing both moisture-wicking and insulation, midweight bases work well with layered apparel. As a midlayer, it also provides a good amount of protection against colder temperatures when combined with medium levels of activity.

Heavyweight (Extremely cold or below freezing temps) - Just by its name says it all. The heaviest base layer is designed specifically for the extreme cold no matter your level of physical activity.

Since heavyweight base layers generally fit looser on the body, they are not typically worn as a first layer but rather worn with lighter fabrics giving it that extra boost of warmth. They are thicker in nature and designed to provide more insulation, not wick away moisture.

A rule to remember - the thinner the material, the better it wicks and the faster it dries. 

Base Layer Styles

As we mentioned above, base layers come in a variety of styles each with their own benefits and suitability. 


No matter how you prefer to enjoy the outdoors, a base layer top is a must-have in the winter for extra warmth or in the summer to help keep you cool. 

Long Sleeve Tops - This base layer style is commonly worn in colder weather and is often paired with additional layers to maximize warmth. 

Short Sleeve Tops/Sleeveless Vests - For the summer or in warmer climates, short-sleeve or sleeveless bases may be more suited for your activity. For a cooler option, consider a vest-style. 

The style you choose will mainly be determined by weather conditions and your personal preferences.


Base layer bottoms are great for adding an extra layer of warmth while enjoying the outdoors. They are extremely versatile and come in two styles: full-length and three-quarter length.

Full-Length Bottoms - A full-length style begins at your waist running all the way down to your ankles. These will provide protection for your entire lower body, especially in cold weather.

Three-Quarter Length Bottoms (a/k/a Boot Cut) - A three-quarter length style fits like capri pants. They start from your waist and hit just below your knee.

While they do not offer the protection of the full-length style, some skiers and snowboarders prefer these since they do not run into the boot which would otherwise create clumping that occurs with your pant legs and socks.

Base layer bottoms are perfect for many outdoor activities, including extreme snow sports, hill walking and cycling. They can be worn under your regular everyday clothes on extra cold days or on their own while lounging.


One-Piece styles are also known as “Onesies” or “Union Suits” and are the ultimate in base layer protection since they seal out any air drafts.

One-Pieces - One-piece styles cover the majority of your body and seals off any wind and snow that would otherwise sneak in, making them perfect for cold weather conditions.

Some prefer this style since it provides coverage across the top/bottom gap with a layer of core insulation without the added bulk at the waist. Oh - and some even come with a hood for more protection.

No matter what your style preference, a base layer will always be directly in contact with your skin and should fit snugly so it can effectively regulate your body temperature through moisture-wicking.

Layering For Your Activity.

There are many different activities you can do that will make you sweat from low-output activities (hiking) to more high-output activities (recreational snow sports).

Certainly, materials are important and will influence your base layer choice. However, there are some materials and weights better suited for specific activities.

Use the guide below as a starting point when choosing a base layer for a more specific activity.

For Low-Output Activities

Casual Hiking - The temperature outside will determine whether you’ll need a lightweight base layer or something that offers a little more warmth.

Any base layer material would work well with the exception of cotton (unless the temperature is milder).

Bamboo is a great material that offers a good level of protection and comfort.

Silk is another good choice with its incredible smoothness, however it does lack a bit in moisture-wicking.

For maximum warmth and comfort, consider a synthetic or wool base.

A base layer with a hood can also be beneficial when hiking since it can offer additional warmth and even some sun protection.

For High-Output Activities

Running - The weight of your base layer will depend on whether you’re running in the summer or in the winter. If it’s only moderately cool outside, start with a lightweight layer and if the temperature begins to drop, opt for a midweight for a bit more insulation.

Synthetic materials are best for running since they are lightweight, breathable and wick sweat more efficiently.

Consider a base layer that is made with thumbholes since this can help prevent your sleeves from riding up as you pump your arms. It can even provide a little warmth and if exposed, a bit of sun protection.

Backpacking - Your base layer should parallel the versatility of your backpacking adventure. If you anticipate being in multiple climates, you’ll need a material that can acclimate like Merino wool and synthetics.

You can disregard your material’s breathability since your backpack is going to trap the heat and sweat regardless. Instead, focus on the weight and comfort of the material.

Wool’s ability to absorb large amounts of moisture without feeling wet to the touch makes it the most appealing option and since wool is naturally odor-resistant, it will help keep you feeling fresh longer, great for those extended treks.

Climbing/Rowing - Engaging in any type of activity requiring upper body strength like climbing can result in lactic acid buildup in your muscles which can cause swelling.  With this in mind, opt for a slightly looser fit which will offer more flexing room for your muscles.

The material should also be on the thicker side and either wool or synthetic would work well since they both provide good protection and moisture-wicking properties.

Recreational Snow Sports - Any activity that has you trudging through snowfields and harsh terrain is definitely going to cause you to burn more calories which is why it’s imperative that you are thoroughly layered to stay warm.

Whether you’re out on the slopes or snowshoeing, you should begin with a lightweight base that focuses on wicking the initial moisture from your skin, followed by a midweight or a heavyweight for more insulation.

As your activity level changes, you can add or subtract a layer but no matter what, you should always have a minimum of one base layer on, preferably something thick and warm like Merino wool. Just be sure it has a snug fit.

A Fresh Tip:   Odor-resistant materials matter, especially during long trips. When engaging in any extreme activity like hiking, climbing or snowshoeing for extended periods of time, it will cause you to sweat - a lot. 

You’re going to want a base layer material that is naturally odor-resistant like Merino wool.

Wool is naturally designed to absorb odor and also has unique characteristics to hide unseemly dirt and grime.

Not only will Merino wool keep you feeling fresh longer, it will keep you dry and warm and should always be your go-to base layer during any extreme outdoor activity. 

Base Layer Features.

In addition to the basics, some base layers will include additional features that may be worth checking out.

  • Thumbholes - These are great in keeping your sleeves from riding up, especially when wanting to remove or add a layer. They also help to keep your hands warmer and if you’re in an exposed area, it can offer sun protection.
  • Loops and Hooks - Perfect for hang-drying that can come in handy while camping, hiking, skiing or partaking in any outdoor activity.
  • Zipped Pockets/Compartments - If you plan on wearing your base layer as a standalone piece, you will definitely appreciate this.
  • Hoodies - Whether you love them or hate them, hoods can provide extra warmth and protection from the sun. It really comes down to personal preference.
  • Zipped Collars - These can be great for on-demand ventilation.
  • Pit Zips/Mesh Panels/Vents - If you’re highly-active, these can offer enhanced ventilation.

Caring For Your Layers.

When you have found your perfect base layer, you’re going to want to make sure you take very good care of it.

Keep in mind that not every material will require the same type of care. Always check your garment’s manufacturer’s care instructions first before doing any cleaning.

Wool   Due to their odor-resistant properties, you’ll be doing a lot less washing and a lot more wearing. 

When you do decide to give your precious woolies a bath, always choose the delicate cycle or wool cycle (if your machine offers it) on a cold/cold temperature to prevent shrinkage.

It’s also best to use a mild detergent that carries the Woolmark logo for best results. Avoid bleach and any fabric softeners.

Never put your wool garment in the dryer. Once washed, it may need to be reshaped and then laid flat to dry naturally. A cool pass of the iron as needed.

Hand washing your delicates is also an option. Just follow up with reshaping and laying your garment flat to dry.

Synthetics   Unfortunately, synthetic materials will require more washing since they are not antibacterial and retain more odor. The good news is that since they are quite durable, they can be machine washed and still maintain their shape.

If your machine offers it, choose the synthetics setting as this will use a lower temperature and be less agitating, protecting the garment from damage. If not, select the lowest setting using warm water.

As for drying, it’s always recommended to hang dry a garment. If you do want to use a dryer, make sure that it’s on the lowest temperature setting.

Try avoiding ironing synthetics. If you do need to press it, use the cool setting and lay a clean towel between the iron and garment to protect it.

Silk   Silk garments should be washed the same way you would your wool garments. You may even prefer to hand wash separately since you run the risk of shrinking it in the washing machine.

Bamboo   In order to maintain bamboo’s special qualities, hand washing is best. Just make sure to rinse the garment well to prevent any staining caused by oxidation of cellulose by the soap residue build-up.

Bamboo can also be machine washed on a delicate cycle in cool water only. A gentle detergent, free of bleach is best. It is also recommended that you do not use fabric softeners or any chlorine bleach as this can significantly reduce its life.

If the garment is of a lightweight variety, line-drying is best. For thicker, heavier garments, they should be laid flat to dry since hanging them can cause the fabric to stretch.

If quicker drying is absolutely necessary, machine dry on a cool setting and remove when slightly damp. Don’t overdry as this can cause damage to the fabric. Be careful when handling wet bamboo fabrics as they are much more fragile while in this state.

Try to avoid dry cleaning any bamboo garments.  Use a cool iron as needed.

For best results, turn your garment inside out before washing, drying and ironing.

Properly caring for your base layers will help maintain its fabric integrity and texture, keeping it just as perfect as the day you first put them on.

Love your layers and they will love you back!

Base Layer Tips.

  • Choose your normal size in base layers as they are designed slightly smaller.
  • Fabrics should cling to your body but not constrict you in any way.
  • Watch out for seams with tags and labels as this can cause irritation and discomfort.
  • Cotton is rotten for your base layer since it does not provide moisture-wicking properties.
  • Lightweight materials are better at moisture-wicking and are quick-drying.
  • Match your base layer with the level of activity to maintain desired body temperature.
  • Base layers are not limited to cold weather; wear them in warm climates to help keep you cool and protection from the sun.
  • Give your layers “TLC” to help keep them looking and performing great.

The Final Layer.

Getting your base layer wrong can be one of the most uncomfortable and even potentially dangerous mistakes you can make.

Remember, choosing the right base layer starts with your individual needs and should always match your activity level and weather conditions.  

So ladies, if you're looking for a quality base layer that will keep you dry, warm and comfortable for all your outdoor adventures, click here and for you guys, click here.

Because no matter how you prefer to enjoy the outdoors, the right base layer will not only keep you comfortable, but in extreme cold conditions, it could also save your life!

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