Learn more about layering by checking out our Introduction to Layered Clothing Systems article that explores what a fantabulous set-up looks like.
Fabric Types and Weights
There is a lot of variety in the world of long underwear. You'll find everything from cheap cotton jumpers to expensive (but cozy) Merino wool onesies. Different types of fabrics offer whole new sets of pros and cons while different fabric weight options are suited for specific temperatures and conditions. So how do you choose the best underwear? Premeditating what you will be using the layer for is your first step, taking into consideration both climate and level of intensity. So before going any further, take a little time to determine what you're looking for in a base layer. Do you want something that will breathe super well? Or do you prefer something with exceptional warmth? Do you want a hood or a zip-up collar? Do you want something you can also wear to work? Take these ideas into consideration, then read on to learn about the different options out there.
Fabrics of Long Underwear - The Pros and Cons
First step. Choose the type of long underwear fabric you prefer. In the world of long underwear, four major categories include Synthetics, Wools, Silks, and Cotton. The highest performance long underwear utilizes either Merino wool or a Synthetic blend. Silk and Cotton are also prevalent but not typically recommended for outdoor recreational use for a variety of reasons. Below we explore the pros and cons of each fabric. Take into consideration the different types and determine what you think is best for your needs.
Garments constructed with synthetic fabrics are often either 100% polyester or a polyester blend. While these garments are typically less expensive and quick to dry, they are often not as warm as Merino wool options. Here is a quick list of the pros and cons of Synthetic competitors.
- Quick to Dry
- Absorbs less water
- Durable (doesn't stretch out)
- Often less expensive
- Easier to layer with smoother face fabric
- Stinky (both long and short-term)
- Petrol-based fibers
- Smaller range of temperature regulation in comparison to Merino wool
- Holds moisture longer when worn (not when drying off the body)
- Not as warm as Merino Wool
- Wet conditions
- Friction-based sports like crack climbing, canyoneering, or bushwhacking
- Where drying quickly is a necessity
- Layering under sticky midweight layers
- Outdoor aerobic activities as a wear-alone piece
Examples of Synthetic Base Layers
- Arc'teryx Rho LT Zip: 84% Polyester, 16% Elastane
- REI Co-op Midweight Crew, our Best Buy award winner, 92% Polyester, 8% Elastane
- Patagonia Midweight Capilene Crew, our Top Pick for Breathability, 100% Polyester
- The North Face Warm Crew, 100% Polyester, 57% recycled
The outdoor industry has come a long way since the age of thick, heavy, and utterly itchy union suits that soldiers would wear on the front lines in the early 1900s. Thanks to technology, and Merino's "ultra-fine" fibers, wool has evolved. It's not itchy, too hot, or heavy, and it is one the best temperature regulating fabrics out there, making it great for all seasons. Not only that - but it doesn't develop a long-term stink!
- Fantastic temperature regulation
- Natural fibers
- Easy Care
- The odor is not an issue
- Warm when wet
- Amazingly comfortable on the skin
- Less durable (stretching and holes)
- Longer time to dry
- Absorbs more water
- Typically heavier in weight
- Typically more expensive than synthetics
- Pretty much everything except friction-based activities that might tear the fabric
Examples of 100% Merino Wool Contenders:
- Smartwool Merino 250 1/4 Zip, our Editors Choice Winner
- Smartwool Merino 250 Base Layer Crew, our Top Pick for Everyday Wear
- Icebreaker Tech 260 Midweight, the warmest base layer tested
- WoolX Hannah
- Kari Traa Rose H/Z
Even though we didn't review any silk blend long underwear, we figured it would be worth the mention. Silk is a comfortable, smooth, and luxurious fabric that is best for cold weather use since it doesn't breathe as well as other fabrics, but it does a decent job of wicking. Save it for cold days sitting in the shade instead of the sunny spring days skinning in the mountains.
- Feels amazingly smooth and luxurious against the skin
- Ample warmth
- Natural fibers
- Very thin and easy to layer
- Not very durable
- Not very breathable
- Needs special laundering care (i.e., hand washing)
- Cold weather lounging
Cotton is widely used because of its low cost. Those who aren't aware of the ramifications may buy these cotton garments from popular stores without realizing what happens when they get wet. In warm, dry weather, they can be amazingly comfortable as they breathe well. That said, it's a highly absorbent material that won't wick, but hold moisture if you sweat or get rained on. If you wear them while in cold weather, this can be dangerous as the moisture is kept close to your skin, ultimately lowering core temperatures. This is where the popular phrase "cotton kills" comes from. As a result, don't be hesitant to use it if you think you'll be chilling out around a campfire. But we wouldn't recommend it for any situation where you might get wet then cold.
- Very breathable
- Feels nice on the skin when dry
- Easy Care
- Absorbs water
- Slow to dry
- Cold when wet
- Camping in warm weather
These are the most common performance baselayer fabrics you'll find in the stores today. Take some time to decide what kind of material you'd love to have as your new base layer.
Choose your Fabric Weight
Next step. Choose the fabric weight you require. There are four different fabric weights to consider when making your long underwear purchase. Each weight refers to the amount of material used in a piece. A more substantial weighted fabric is better suited for cold weather (as there is more insulation) than a lighter weight fabric that is better suited for warm weather (there is less insulation). There are four primary fabric weight designations that include Microlight, lightweight, midweight, and heavyweight. Through this section, consider what you will be using your base layer for. If you want versatile and multi-functional use, we suggest midweight layers.
All the layers tested in this review fall into the mid-weight category. Each piece that we tested typically has either a lighter or heavier weight option. Be sure to look through all weight options before making your decision.
The lightest of the lot, this super lightweight fabric is meant for providing sun protection during the warmest seasons of the years. They are constructed of ultra-thin materials that are perfect for running in the warmer weather of the spring, summer, and fall.
Perfect for warm weather that has a little nip in the air. This lightweight option is a tad warmer than the micro lightweight fabric and ideal for wear-around use when temperatures are warm. When the mercury plummets, this weight shirt may be perfect for a spring or fall run in cooler temperatures. It's also an excellent option for warmer winter days where you might find yourself hiking uphill for a few hours.
A tremendous all-around weight suited for extended backpacking trips and day excursions to the local ski hill. This weight will keep you warm with a proper layering system in winter storms down to double negative digits. On warmer days, this weight might regulate well keeping you comfortable in temperatures up to 60 degrees when wearing a garment on its own. All products in this review fall into this category.
If you plan on hitting the most Polar places on Earth, a heavyweight layer is best. Best suited for frigid temperatures and frigid conditions, this weight layer is very thick and can even be worn as its own insulating shirt in cooler conditions. We'd recommend it if you're seeking a warmer wear-alone top or if you are going to be hanging in the double negatives on a regular basis.
In addition to choosing the correct weight and type of fabric, the fit is a huge consideration. In our reviews, we provide depth as to the fit of each garment. A piece that is long enough to provide coverage that hugs you in all the right places is a serious consideration. You don't want to buy something that is uncomfortable because you simply won't wear it.
You know that saying "fits like a glove?" Well, that applies here. Base layers are meant to cover you and stay close to your skin. You don't want something that is skin tight making you uncomfortable. Also, you don't want a shirt that's too baggy, or it won't wick properly. Ideally, you want to be able to layer clothes overtop this layer or put a small tee underneath (in case temperatures rise).
One of our pet peeves is when a top is too short in either the arms or torso. When hiking or playing in the great outdoors a shirt that rides up is annoying. To avoid this, make sure your new shirt has a little stretch and is long enough to cover your body. This can be ensured by reading our reviews to get the low-down on the comfort and fit of each piece. Overall, make sure your shirt fits!
If you're unsure about ordering online, make sure you purchase from a dealer with an easy return policy. This way you can try things on and send them back if you don't like them.
What features should you consider? Long underwear tops come with a diversity of different features. Some are super simple without any, while others come loaded with thumb loops, hidden pockets, hoods, and more. Some shirts feature different styles that offer different function. Before buying, consider the type of style you prefer and the different features you'd love to have!
Thumb Loops are nice to have because they create an anchor point for your sleeves. Some people love them while other people hate them. Regardless, they are an excellent addition that makes the layer more versatile. When layering over other tops, you can slip your thumb into the loop to help pull down the fabric of the arms. The only shirt in this review with thumb loops is the Patagonia Midweight Capilene Crew.
Pockets are super sweet. A little stash place for car key, credit card, or Kleenex is quite convenient while out on a jog around town. Our testers liked them for long trail runs and skinning adventures in the mountains. Sometimes they are located in a hidden pocket on the hem while other times they might be found on the arm or breast. The only layer that incorporated one in this review is the Arc'teryx RHO LT Zip.
UPF (Ultraviolet Protection Factor) might be another factor to consider when purchasing a base layer. If you plan on being in a super sunny spot like a glacier or the desert, UPF might serve you well. Ultraviolet light can penetrate through most thin fabrics and can still cause some sun damage. So if you're interested in protecting your skin or you are sensitive to the sun, find a layer with a UPF factor of at least 40+ like the Smartwool Midweight 250 Crew.
Hoods are another feature to consider when looking at a base layer. Most don't come with a hood as they are intended to go beneath all your clothes and might add extra bulk; however, a hood also adds versatility. None of the pieces we tested incorporated a hood, but there are many out there!
Different Collar Styles
Crew Necklines are great for layer combinations where you have neck protection like a neck gaiter incorporated. They are also great for days when it's not too cold outside since they allow a little more breathability. Most of the layers we tested incorporated a crew neckline. We find that these necklines are not as versatile as the zip-up neck options though.
Zip Necklines is a little more versatile since you can choose to stay unzipped for normal days out or to zip-up when the wind kicks up. Zip neck options tend to be a tad more expensive and add a little more bulk.