The Best Long Underwear for Women Review
We tested seven of the industry's best long underwear shirts as both stand-alone tops in warmer weather and as a base layers in colder weather. These tops went on all sorts of adventures, including multi-day backcountry ski hut trips, sandy trail runs through the desert, rock climbs on the colorful walls of Nevada, and numerous walks down the river trail in hometown Ridgway, CO. After our field testing, we got down to the knitty gritty, rating each top on warmth, breathability, layering ability, comfort & fit, drying speed, and durability. Although many layers performed well, a few special pieces really stood out.
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Test Results and Ratings
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Analysis and Award Winners
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Analysis and Test Results
For any avid adventurer, long underwear is the base of a functional layering system. Start with a non-cotton pair of panties and a bra, add a wicking base layer (aka long underwear), sprinkle on some insulation (an insulated jacket for women, perhaps?) and top it off with a shell and you've got yourself a solid outdoor layering system. Of all the ingredients in this outdoor recipe for fun, your wicking base layer could arguably be THE most important layer you choose for comfort in the hills, especially if you're out for days on end. You don't want a layer sitting next to your skin that is itchy, fits funny, or collects moisture that could effectively lead to your demise if a sharp wind picks up. You should look for something that feels comfortable, doesn't chafe, covers your whole torso, and something that looks good (you are bound to wear this on its own!). Odor is something else to consider and we'll definitely talk about that in just a bit. If you can get all these things in a base layer, you will find yourself with high morale tackling any mission.
To learn more about layering systems in depth, check out our Introduction to Layered Clothing Systems article that explores what a truly fantastic set-up looks like.
Not only are long underwear tops useful in a layering system, but are also great as a stand-alone pieces. In warmer weather, they can serve as a top while hiking, climbing, or even running. Many tops are designed to wear alone and have cute colors, stylish lines, and flattering fits. When you are shopping, opt for a top that looks and feels as good on the outside as it does layered underneath other clothing.
This article focuses on long underwear tops ranging from lightweight to midweight; the products in this review are appropriate for all seasons except for truly frigid temperatures. If you're looking for shirts that are great for aerobic activities, check out women's running shirts. Or if you're looking for a warm mid-layer, check out the Women's Best Fleece Jacket Review.
Types of Long Underwear
In the world of long underwear, there is a lot of variety. You'll find everything from full cotton jumpers to really high tech wicking underwear with fancy features like built-in gloves and lavish hoods. You'll find different fabric weight options suited for different weather conditions, different types of fabrics with their own sets of pros and cons, and a medley of other features. So how do you choose the best underwear for your ambitions? Premeditating what you will be using the layer for is your first step - both climate and activity level should play into your decision.
If you're planning on using this layer during aerobic activity in the spring or fall then you might consider lighter weight long underwear; midweight layers are often perfect for winter aerobic activities. On the flip side, if you're planning a winter camping trip and will spend less time being active, then a heavier and thicker layer might be your best option.
Once you've determined how you'll use your long underwear, consider the fabric type. Most types fit into one of the following categories: synthetics and synthetic blends, wool, and silk. We explore the pros and cons of each one in our Buying Advice article. Once you know your fabric, determine what features and cuts you're interested in. Do you enjoy high collars and zip up vents, hoods, and/or thumb loops? Once you've got that determined, look at the selection offered in this article and see what suits you best in style and fit. In the next part of this article, we'll cover a few of these topics more in-depth before diving into our Criteria for Evaluation.
Every fabric weight has a different purpose and you'll notice at your local gear store that different long underwear weights that are meant for very specific purposes. Here, we outline the four major fabric weight categories:
Micro Lightweight: Meant for warmer weather and aerobic endeavors like running during the warmer seasons of spring, summer, and fall. These shirts are delicate with extremely thin fabrics that are ultra lightweight. Wear these tops on your favorite run or a cool summer night.
Lightweight: Perfect for warm weather that has a little nip in the air. The lightweight option is a tad warmer than the micro lightweight fabric and not super optimal for aerobic pursuits unless the mercury has dropped. This fabric thickness is ideal to be worn as a stand-alone layer during cool days, or as a layered friend on warmer winter afternoons. The Icebreaker Oasis - Women's is an example of one of the lightweight tops we tested.
Midweight: A great all-around layer suited for long backpacking trips and day excursions to the local ski hill. These tops will keep you warm with a proper layering system in winter storms down to 0 degrees F. In warmer weather they are still able to regulate quite surprisingly to keep you comfortable in warmer temps up to 65 degrees F. Most of the products we tested fit into this category including our Best Buy Award winner, the Patagonia Capilene Midweight, and our Top Pick for Comfort, the Smartwool NTS.
Heavyweight: Best suited for really cold temperatures and frigid conditions, these base layers are very thick and in many cases can be worn on their own as an insulating shirt in warmer weather. We didn't test any in this review.
In general, common long underwear materials include synthetics, merino wool, and silk. Synthetics are manufactured with materials like polyester, elastane, and spandex and are produced by companies like Patagonia, Hot Chillys, and Arc'teryx. In general, they dry very fast, are easy to care for, and fit in a variety of ways. One big downside is that they aren't as warm as Merino wool blends and they begin to smell after multiple days of use. If you've owned a synthetic version for a long time, chances are high that you've noticed that smelliness can linger and that it is very difficult to get rid of, unless it has an odor blocker. Most of the synthetics we tested had an odor resistant additive like Polygiene incorporated into the fabric.
Merino wool long underwear tops are manufactured with natural materials and, as the name suggests, made with 100% merino wool, varying in the quality of fibers. Outdoor manufacturers like Smartwool, Icebreaker, and Minus33 are leading producers of these garments. Merino is awesome because it's natural, odor-resistant, typically warmer, and regulates temperature really well.
For a full breakdown on what the differences are between these fabrics, visit our Buying Advice Article. In all cases, these fabrics, unlike cotton, will wick moisture away from the body, protecting you from hypothermia when winds pick up and the mercury begins to plummet. So how does this wicking work ??
Wicking is wonderful science!
Wicking refers to a little something called capillary action where air molecules seek out an equilibrium by moving from areas of HIGH humidity to areas of LOW humidity. In this regard, synthetic and wool fibers work in different ways. Synthetic fibers are effectively non-absorbent plastic and they allow water vapor molecules to pass easily through to the other side of the fabric. The vapor is moved based on these humidity differences (aka a humidity gradient). Merino wool, on the other hand, will actually absorb the moisture and it will evaporate on the other side due to a moisture gradient (higher moisture inside versus outside), sunlight, and airflow. Cool huh?
So here's an even more in-depth breakdown. You are out on your favorite trail run and it's cool enough to don your favorite base layer. Let's just say your favorite is a synthetic fiber. As you move, your skin heats up and starts to produce sweat. As you produce sweat and heat, the air molecules expand, changing from a liquid to gaseous state (i.e. water vapor). As more vapor gathers, you create an environment of HIGH humidity between your skin and your base layer. Now imagine all these molecules, crowded, clamoring for space. They look up to see a lattice of non-absorbent fibers that they can pass through to get to an area that isn't as crowded. As a result, they pass through this lattice and move to the outside of the shirt. This is how wicking equals temperature regulation! Because these fibers are "plastic compounds" and don't absorb water, they will dry out quickly, especially when you are active and there's a wind present.
Merino wool on the other hand does not have that lattice of plastic fibers. Instead it is a collection of fine and absorbent fibers with a rough exterior called the "cuticle" that is overlaid with a waxy and water resistant "epicuticle." There is magic here. As your body produces heat and you begin to sweat you emit water vapor. In normal circumstances after this water vapor (gas) is emitted it will cool and condense forming water droplets (i.e. sweat). Merino wool acts to pull moisture vapor into the fabric where it evaporates before it can condense leaving you feeling dry. The Icebreaker website states that a merino layer can effectively hold 30% of its weight in water before you start to feel wet. Cool huh? Not only that, but the epicuticle will resist water in its liquid state. It won't saturate until it is exposed long enough and has been really agitated.
If you are a sweaty person, merino wool may be a great choice for you. Even though it might be heavier weight, it will probably feel more comfortable and warmer against your skin than a synthetic. On the flip side, it's important to note that synthetics are known to be super light and dry out very quickly.
Take a look at this video by Icebreaker to learn about the differences between synthetics and merino wool. They focus on Icebreaker technology, but this similar to how all merino wool works.
So there's your high school science lesson. We'll continue discussing the pros and cons of wool and synthetic throughout the review, but this should give you some great starting knowledge. In our own investigations, the comfort and breathability that we observed tracked with this science. Keep reading to see how we put each garment through a head to head tests outside and in controlled settings.
Criteria for Evaluation
Over three months, we called upon many women to test these long underwear tops in a wide range of temperatures in a variety of places. To determine our testing criteria we talked to numerous mountain guides, runners, and outdoor enthusiasts about what they thought the standard for a base layer looks like. Our top responses are reflected in our metrics: Warmth, Breathability, Layering Ability, Comfort & Fit, Drying Speed, and Durability.
When choosing a long underwear top, warmth is one of the most important factors to consider - that's the primary reason to wear one in the first place! Having a base layer that will keep you warm means that you will be comfortable and happy! The first point to consider is the weight of the layer. Basically a heavier weight = more warmth as a result of more insulation. In addition to fabric weight, we discovered that there are a few other things that contribute to the overall warmth of a long underwear shirt. The first is its ability to cut wind (not completely, but a little bit!) when worn as a stand-alone shirt.
Some shirts have tightly knit face fabric that do a great job of locking in warmth by not allowing wind cut through it. When it's layered up, this doesn't matter nearly as much because your outer layers serve this purpose.
Which brings us to our second point: when you do have a layered system, it is very important that the fabric wicks or is able to transport your sweat away from your skin when worn next to skin. If a fabric is unable to do this, that sweat will eventually cool down which will inevitably drop your core temperature. If you are in a cold temperature with cutting winds, this can create a life threatening situation and could lead to hypothermia. This is why cotton is not a good base layer in cold temperatures because once you sweat, it keeps that moisture next to your skin. Consider all these points when considering warmth as a metric.
In general, one thing that we did notice was that the merino wool long underwear tops including the Smartwool, Oasis Crew, and Minus33 kept us the warmest when we lazed about in cool to cold weather - inside our apartment and outside while camping. The fibers of these merino wool tops seem to actually generate more heat to keep you warmer than its synthetic competitors. The Smartwool Midweight Crew scored highest in our warmth metric for its ability to keep us warm and cozy while lazing around in frigid temperatures. Not only that but it also released heat sufficiently - earning a 9/10 in this area. The Arc'teryx Rho LT Zip - Women's also earned a high warmth score, especially since the tight weave on the face fabric really helps block the wind. Tops like the Under Armour Base 2.0 Crew - Women's weren't as warm as the Arc'teryx or Smartwool, but are a great option for folks looking for a layer that can regulate temperature during more aerobic adventures.
In a base layer, breathability is very important when it comes to temperature regulation. What does that mean? It means that breathability plays a key role in keeping you warm when it's cold outside, and keeping you cool when it warms up. A shirt that is able to get rid of heat quickly is awesome, but sometimes if it gets rid of that heat too quickly, it's not as warm.
An optimal base layer will let heat exit when temps rise and you start to sweat, but it will not be so breathable that it allows warmth to escape when you stop moving or temps start to drop.
If you are looking for layer to use for aerobic activities, however, a base layer with high breathability may be just your ticket. If you're looking for an all-around layer, look at shirts that share ratings that have both high warmth and breathability ratings. It's important to note that all the tops tested breathed quite well, so the differences between shirts aren't that great and should be taken with a grain of salt. Of all the layers tested, the Under Armour Base 2.0 Crew - Women's, was definitely our breeziest layer, taking home a 9/10. Its fabric easily allows moisture to move from the interior to the exterior as a result of its waffled fabric. Though, it's important to note that its breathability did come at a price of low warmth.
On the other end of the scale, we awarded the Arc'teryx Rho LT with the lowest breathability rating. We found that while climbing in Red Rocks it cut the wind and maintained heat well while sitting at the belay. When we were climbing we definitely felt the fabric breathe and it wicked moisture well. However, when performing more aerobic activities like running, nine times out of ten we had to take it off. We thought this was perfectly acceptable as most of our running was done on warmer days, and to be expected for most midweight layers. That said, it is still breathable but not as breathable as layers like like the Hot Chillys Micro-Elite Crew - Women's.
While these base layers will presumably be the "next-to-skin" layer, it is an added bonus when you can wear a tank or tee underneath if you expect conditions to warm up. Not only that, but you want to make sure that you can throw layers over top and remove them without getting a whole bunch of static electricity buildup that causes the garment to ride up and get uncomfortable after long stints outside.
Surprisingly, the Smartwool Midweight Crew actually took home one of the lowest ratings for layering. This is primarily because of the static cling that we experienced numerous times when trying to layer a Patagonia R1 - Women's on top of it. The sleeves clung, got stuck and provided us with frustrating moments of trying to straighten out the materials. All other shirts performed better in this department except the Under Armour Crew 2.0 due to its thicker composition and incredibly rigid structure.
Fitting layers under and over the Arc'teryx Rho LT Zip was EASY! Not only that but both sport incredibly long torsos, which our testers (with varying chest sizes) loved. Unlike the Smartwool NTS, changing out layers was hassle-free with these two top-scoring layers.
Comfort & Fit
Ah, comfort something that every women needs and craves. Comfort and fit are two peas that make up a luxurious pod when just right. Cozy fabrics, long lengths, versatility, and "like-a-glove" fit is what we looked for when scoring this category. In most cases, this testing was the easiest - lazing about watching movies, hanging out around the campfire, going out with friends, and seeing how fabrics feel after day four of constant wear with no wash. With that in mind, we also factored odor build-up into the scores for this category.
Taking home the Top Pick for Comfort is the truly cozy and cuddle worthy Smartwool NTS Midweight Crew. It features 250 g/m3 of natural New Zealand merino wool, a bit of stretch, and thick cuffs and hem lines. Even though it wasn't as long as layers like the Arc'teryx LT Zip, it provides a great fit perfect for women of all sizes. The Icebreaker Oasis and Under Armour Base 2.0 Crew were on the other end of the scale. The Icebreaker's fit was too short and rode up on most of our testers to expose skin. The Under Armour Crew's fit was just too rigid and didn't fit a lot of the women that tried it on, in fact, most reported that it felt tight in the shoulders. In terms of odor, we noticed that the merino wool blends were significantly more resistant to body odor than the synthetics. None of the shirts have showed signs of lingering smell yet but from prior experience, we anticipate that synthetic compositions like the Patagonia Capilene Midweight will start to smell after a year or two of use.
Being stuck on a mountain in a torrential downpour can be a fun, exciting experience that you will never forget or it can be the opposite. Regardless of your attitude towards this particular situation, it's important to make sure that your base layer will perform in the face of mother nature's worst moments. That means that it will not only remain insulating if it gets wet, but that it will also dry out quickly when the skies turn blue again. You don't want to be stuck on a multi-day backpacking trip on the Pacific Crest Trail with a layer that doesn't dry quickly enough, keeping you cold and miserable. To evaluate this metric, we went hiking in the rain and checked to see which ones were 1) more impervious to rain; and 2) which one dried out the fastest. We also performed a drying speed test in a controlled environment to really see which performed the best. To start, we threw all the layers in the washing machine without any extra spin cycles. We then did two hang to dry tests. One inside (very controlled environment) and one outdoors (to simulate hanging them in a tree on a multi-day hike). Our results were interesting, but not surprising.
Checking each garment every 20 minutes we were able to monitor which layer dried the quickest and which took the longest. We found the same results for both of our tests. One general pattern we noticed was the synthetic layers dried faster than the merino wool layers. Of these synthetics, the Under Armour Crew dried incredibly fast - and almost came out dry from the washer. Within the first 20 minutes it was already dry. Following the Under Armour was the Arc'teryx Rho and Patagonia Capilene Midweight, which dried at a similar rate. Following this was the Hot Chillys Micro-Elite. The Smartwool and Icebreaker were next, with the Minus 33 layer trailing along at the end.
These results aren't surprising as the Under Armour sports a waffle fiber that allows ample airflow in trade-off for warmth. The merino wool taking longer wasn't surprising either, as the fibers are designed to absorb water. However, during our tests, we also found that merino wool was more impervious to water in the first place, so it takes a little while longer for water to absorb when it starts raining.
If you're planning on participating in a long trek where you might encounter rain, a synthetic layer like the Arc'teryx Rho or Capilene Midweight may be a better choice than a slower drying merino option like the Minus33.
A really great layer should last a few years or more, depending on use and abuse. It shouldn't shrink, stretch out, or pill after just a few months. Additionally, we don't think that you should see fly away stitches within the first three months of ownership; as a result, we docked products durability points if we saw any. With prices ranging from $50 to $130 it's important to know this piece will last. To look at durability, we inspected shirts for fly aways, noted quality stitching, and noted any signs of wear and tear. We also looked at whether any of the garments shrunk and if any lost their ability to regulate temperature.
In our observations over the last few months, we found that our merino wool layers need to be treated a more carefully than their synthetic competitors. In our tests, we found that the fibers in our merino wool pieces tended to snag and pill more easily. However, when comparing stitching, we noticed that some companies chose to use less durable thread that was more susceptible to pilling.
Overall, we found that the Arc'teryx Rho LT was extremely well-constructed - after three months of heavy use, there were no fly away threads or signs of wear and tear.
We were equally impressed by the Hot Chillys Micro-Elite. Every other piece showed some sign of wear and tear. We were especially disappointed with the Smartwool piece. Not only did we observe excessive pilling, but also a hole developed on the right shoulder. If you're looking for a more durable merino layer, check out the Oasis Icebreaker Crew. Two final things to note. No shirts lost their ability to regulate temperature, but we did note shrinkage with the Oasis Icebreaker and Under Armour Base 2.0. If you buy these, make sure you either hang to dry or size up upon purchase.
Completing Your Layering System: Long Underwear Bottoms
Long underwear bottoms are a perfect complement to any cold weather layering system. If you plan on participating in any cold weather sport, it's imperative to add base layer bottoms to your "must have" winter gear list to keep you warm and safe. Similar to base layer tops, performance bottoms wick moisture away from your skin effectively keeping you warm when the temperatures dip below freezing.
Choosing a pair of bottoms is similar to choosing a top: take into consideration the weight of the fabric, the material, and the cut. When looking at fabrics, make sure you check the packaging to ensure there is no cotton and its fabric is composed of merino wool, synthetic, silk, or a blend. The pros and cons for each of these fabrics are the same as we discussed in our Buying Advice guide. For weight, consider the activity you will be participating in to decide what weight to choose. For example, if you live in Northern Minnesota and plan on hunkering down to ice fish all winter, look at a heavy weight option. If you plan on hiking a lot, choose a lightweight option. Remember that these bottoms are a little different then tops since you won't be able to take them off easily if you're too hot. Last but not least, consider the cut. In general, you can choose from 3/4 and full pant options. Choose a 3/4 length for activities where you might wear high socks like skiing. Choose a long pant option for everything else.
Most long underwear tops have a complementary bottom made with similar material, often with different cut options. For your shopping ease, we have included these options at the bottom of each individual review.
The Coolest Original Feature Award, Non-Performance-Related, goes to the Icebreaker Oasis - Women's for its traceable sheep donor project. What can we say besides Baaaahhhddddd-ass!
Knowing what base layer to purchase can be difficult. Fabric, weight, and style are only a few of the features to consider when choosing the right long underwear for you. The pieces in this review work as a vital part of a layering system and can be worn on their own as well. Read through our Buying Advice article for more information on the different fabrics and cuts that are available to find the best option for you.
— Amber King
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