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How to Choose the Best Long Underwear Bottoms for Women

By Amber King ⋅ Senior Review Editor
Monday November 19, 2018

Perhaps one of the most important pieces of gear to consider is the one that sits next to your skin. A great piece of long underwear (or a base layer) does its job by wicking away moisture and transporting it away from your skin to ensure that you stay dry. This is monumental to ensure that you stay warm during cold spells after moving for long periods of time. In this buying advice article, we focus on what you should consider when buying a bomber pair of long underwear bottoms. The first thing to consider is what you need this important piece of gear for. Once you've clearly defined your use, consider a few key factors. Take a look at the fabric, its weight, and finally, fit and style. When learning about these important considerations, you'll be ready to purchase the best long underwear bottom for your purpose. Whether it's crushing the backcountry on a pair of skis or sleeping out under a summer night sky in the desert.

There are many different options out there. Which one is best for you?
There are many different options out there. Which one is best for you?

Long Underwear Fabrics


A great pair of long underwear bottoms is made from either merino wool, synthetics, silk, or a blend. When looking at a great base layer, take a look at the fabrics that your bottom is built from. Each has its own unique set of pros and cons.

Merino wool trumps synthetics in the way of overall performance and comfort. While its not typically as durable  it dries out quickly and is better used for wear...many days on end. Here we take a jog around a lake in Canada  staying warm and comfortable in freezing conditions.
Merino wool trumps synthetics in the way of overall performance and comfort. While its not typically as durable, it dries out quickly and is better used for wear...many days on end. Here we take a jog around a lake in Canada, staying warm and comfortable in freezing conditions.

Avoid cotton blends or 100 percent cotton fabrics. These fabrics are dangerous and do not dry out after sweating or if they get wet. If you find yourself in a situation where you are wet and cold, it will not keep you warm. There is a reason that the age-old saying "cotton kills" is true. Avoid it at all costs, even though it's cheap.

Merino Wool


You can't go wrong with a 100 percent merino wool base layer bottom. Like all great base layer fabrics, it insulates when wet and it is extremely cozy and comfortable. Merino wool is not itchy (even when wet) and can provide all-day wear comfort. To boot, it also has an exceptional range of temperature regulation and will keep you dry. The materials have an awesome affinity to breathe, transporting moisture off your skin and out of the fabric. The fabric does not hold moisture. An added bonus is it doesn't stink…even after being worn for days on end without a wash.

The Merino wool fabrics are soft to the touch  offering ample comfort for all-day wear.
The Merino wool fabrics are soft to the touch, offering ample comfort for all-day wear.

While merino wool is typically the best quality when it comes to performance and thermoregulation, it does have its caveats. Given the soft and supple design of the fabrics, it is typically not very durable. A simple fall or a brush against a sharp branch can cause a small hole. The material also can absorb more water than a synthetic. That said, it does dry quite fast. Not to mention that merino wool is typically a lot more expensive than synthetics. Those caveats aside though, it simply does provide the best performance on the trail when compared to synthetics. It is a great option for all types of weather and conditions.

Examples: Smartwool Merino (250/150) Bottom, Icebreaker Oasis Leggings

Synthetics


Synthetic long underwear is typically constructed of either 100 percent polyester or some form of blend that might integrate elastane, rayon, or other materials to help promote durability, wicking ability, and/or elasticity. Synthetics are great as they are typically less expensive and more durable than merino wool. The material performs well by wicking away moisture and keeping your relatively warm when wet. In addition, this material is typically easier to layer as the face fabric is smoother and thinner.

Synthetic fibers are much more durable  offering use for many years.
Synthetic fibers are much more durable, offering use for many years.

Synthetics are great for many purposes, but when comparing it to merino wool, it simply doesn't stand up. The fabrics aren't as soft or as cozy nor are they as warm after being sweat in. The material typically holds the moisture a little longer, ultimately making the layer a little colder if running for a stint then slowing down in cold weather. Overall, thermoregulation ranges aren't as wide…but the fabric still performs. In addition, synthetics typically start to smell if being worn after a few days of not washing. While many brands offer "odor-resistant" finishes, they typically don't work if you've begun to reek and haven't been able to shower for a few days.

Examples: Patagonia Capilene (Midweight/Lightweight), REI Co-op Lightweight Base Layer Tights

Merino-Synthetic Blends


Just recently, companies like Patagonia have been manufacturing revolutionary technology that infuses the benefits of both merino and synthetics into one type of fabric. For example, the Patagonia Capilene Air Bottoms have a blend of the two fabrics. This offers an exceptional level of comfort and thermoregulation. In addition, this design offers stand-out durability and drying speed. While we didn't review these base layer bottoms, we are excited to see where this new technology takes base layer bottoms.

Silk


While we didn't review any silk options, you might find a variety of silk-based long john bottoms out there. Silk is renowned for how soft it feels against the skin. Its slippery face fabric fits nicely underneath other layers and is super thin. It doesn't breathe exceptionally well, but the material will wick just fine. It's a great option to add to an already useful base layer set-up if you're looking for a little extra wicking power. The only issue is that its fabric will absorb your trail stink. So wash it every time you wear it.

Weight


Now that you've taken the time to determine the type of fabric you want, the next step is to look at the weight of fabric you might need. Many companies offer a variety of fabric weights to reflect the relative amount of warmth and breathability you might require from a base layer. A lower weight means that there is less fabric used meaning a higher level of breathability and a lower amount of warmth. A higher weight exemplifies the opposite, a lower relative level of breathability and a high level of warmth.

Where are you going to play? Consider the climate and weather you'll be encountering to determine the weight you require from your long underwear bottom.
Where are you going to play? Consider the climate and weather you'll be encountering to determine the weight you require from your long underwear bottom.

Two key considerations are whether or not your run hot or cold, and what level of activity you plan on taking on. If you're a cold person, opt for a thicker layer. If you're planning on sprinting through the snow on your next pair of snow skates, then opt for a thinner layer. Also, keep in mind that a base layer's job is moisture management. If you run cold, its best to opt for a thicker mid layer or warmer insulated jacket.

Lightweight


Made of ultra-thin materials, this base layer is best for high output activities or just cool days where the sun might show its face. Layer this under a warm insulating layer for great wicking capabilities. The thinner construct makes it easier to fit underneath more layers than a thicker construct. Best for aerobic or high output activities on cold days, or as a simple base layer on warmer winter nights.

A look at the ultra-light Smartwool 150 constructed of thinner fabrics and thus offers better breathability.
A look at the ultra-light Smartwool 150 constructed of thinner fabrics and thus offers better breathability.

Examples: REI Co-op Lightweight Base Layer Tights, Patagonia Capilene Lightweight Bottom

Midweight


This is the most versatile of all weights. Its warm enough to keep you toasty is sub-zero temperatures and can be worn on its own on warmer days. The fabric is a little thicker and offers great insulation in cold conditions. It still breathes and wicks well, providing warmth for lower output activities like day hiking or snowshoeing.

The Smartwool 250 offers thicker fabrics that are still breathable but offers better warmth then thinner fabrics.
The Smartwool 250 offers thicker fabrics that are still breathable but offers better warmth then thinner fabrics.

Examples: SmartWool Merino 250 Bottom, Icebreaker Oasis Legging

Heavy or Expeditionary


The heaviest and thickest of all base layers. We would only recommend this thickness for seriously polar conditions or if you're seeking a base layer that can be worn on its own (without another layer) on cooler days. While the fabric still breaths and wicks well, it's very warm and thick. Layering is possible, but harder then thinner base layer constructs. We did not review any heavyweight options in this review, though some of the bottoms reviewed offer this weight.

Fit Features


In addition to fabric type and weight, you should also consider the fit features of a long underwear bottom. Many women hone in on important details that could make or break a pair of long underwear bottoms. Here we discuss important fit features such as what to look for in overall fit, different length options, waistband details, seams, and calf fit.

A look at the overall fit of the Patagonia Capilene. While base layer bottoms are pretty simple  it's important to look at a few key features.
A look at the overall fit of the Patagonia Capilene. While base layer bottoms are pretty simple, it's important to look at a few key features.

Overall Fit


You should buy a pair of long underwear that fit close to the skin. Its main job is to wick away moisture, which can't be done if the material is baggy or falls away from your body. Also, while on your search, look for bottoms that don't stretch out too much while running or on the move. Merino wool blends sadly do this a lot, but synthetic options do a better job keeping close to your skin throughout the day.

Length Options


There are a few different options when it comes to length. Some women prefer a full length fit while others perfect a three-quarter length option. Full length offers full coverage and ultimately more warmth and breathability. However, some women prefer better ventilation which is offered in the three-quarter length option. Another fun option is the full body onesie! Some manufacturers actually offer long underwear that extends from a top all the way to the bottom. These are incredibly warm and comfortable…but don't offer the best versatility when it comes to ventilation. That said, when considering the kind of long underwear bottom, ask yourself what kind of cut you prefer.

REI Co-op Merino Wool
REI Co-op Merino Wool
Smartwool 250 Midweight - good mid-length.
Smartwool 250 Midweight - good mid-length.
Patagonia Capilene Lightweight
Patagonia Capilene Lightweight

The Waistband


A comfortable waistband that fits well is super important. We noticed that some waistbands are a little itchier than others and don't offer the same level of comfort. When perusing through different options in this review, make sure to take note of which waistbands offer a little more in the ways of cozy fabrics and elastic design. You don't want a waistband that will stretch out over time or doesn't feel good next to the skin.

Some waistbands are more comfortable than others. This Smartwool 150 has a padded interior that feels more comfortable against the skin than other contenders.
Some waistbands are more comfortable than others. This Smartwool 150 has a padded interior that feels more comfortable against the skin than other contenders.

Flat Seams


A quick note here, but always make sure that your long underwear has flat seams. Since the fabrics sit right next to the skin, a seam that isn't flat will cause discomfort and chafing over time. Typically super cheap base layers that you might find at your local department stores will not have flat seam technology. That said, make sure your base layer integrates this. Every piece in this review has flat seams that are comfortable and cozy next to the skin.

Flat seams are offered in all the products tested  however  some are more comfortable than others. Be sure to look at how flat the seam is...the flatter the better.
Flat seams are offered in all the products tested, however, some are more comfortable than others. Be sure to look at how flat the seam is...the flatter the better.

Calves and Cuffs


If you spend time crushing hills outdoors then you've probably got a killer set of calves. While big calves are sexy and powerful, sometimes base layer bottoms will have a hard time accommodating them. It's important to look for base layers that have "stretchy fabrics," especially around the calf and ankle. When shopping, yank on the cuffs to see if they stretch. If they don't and they look a little too thin (or big) move onto the next option.

The cuffs at the bottom should stretch. This provides a versatile and comfortable fit...especially for ladies with larger calves or ankles.
The cuffs at the bottom should stretch. This provides a versatile and comfortable fit...especially for ladies with larger calves or ankles.

Layering Advice (On-the-go)


Layering can be an honest work of art. You need to balance the amount of energy output and ventilation you require from your gear. This means considering what you're going to wear as a base layer, insulative mid-layer, and jacket. As far as long underwear is concerned, it's important to make sure your baselayers breathe. If you know that you're going to be pushing it in super cold weather, be sure to purchase mid layers or a jacket that offers good breathability and ventilation. While a good base layer wicks away moisture, the moisture needs to be able to leave the fabric by means of appropriate ventilation or transfer to your mid-layer and out of your jacket. This important transfer will ultimately keep you warm and dry when on the move. Sometimes this means stripping down to your baselayers and other times it simply means opening up the pit zips on your jacket. Remember, your outdoor wear is a layering work of art. Make sure you purchase the correct mid layers and jackets for the temperatures, conditions, and level of output you'll be putting your body through. Then get ready for some seriously awesome adventures!

Whether you're ice climbing  hiking  skiing  or just sitting around a campfire  an appropriate base layer system is key to keeping you warm. Make sure your insulative layers provide good ventilation while your base layers wick away moisture.
Whether you're ice climbing, hiking, skiing, or just sitting around a campfire, an appropriate base layer system is key to keeping you warm. Make sure your insulative layers provide good ventilation while your base layers wick away moisture.

Conclusion


Now that you've taken the time to consider the best fabrics, weights, and features of your next pair of base layer bottoms, take a look at the options out there. Our Best Long Underwear for Women review will help navigate you to the best options that are currently on the market. We hope that we have been helpful in your quest for one of the most important pieces of clothing to have while tackling stellar adventures in the backcountry.


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