Smartwool Classic Thermal Merino Bottom
A person wearing Smartwool Classic Thermal Merino Bottom long johns, highlighting their comfortable fit and merino wool material
$115 at REI (before member cash back!)
OVERALL SCORE: 76
- Warmth 9.0
- Breathability 7.0
- Comfort and Fit 8.0
- Durability 7.0
- Drying Speed 6.0
- Layering Ability 7.0
Materials: 100% Merino wool | Weight: 7.6 oz (size Medium)
REASONS TO BUY
- Exceptionally cozy and comfortable for all-day wear
- Excellent thermoregulation to maintain ideal body temperature
- Features a merino wool-lined waistband for added comfort
REASONS TO AVOID
- Can stretch out after multiple wears before washing
- Higher price point compared to other options
The Smartwool Classic Thermal Merino Bottom earns our top recommendation as the best overall long johns. When temperatures plummet, the combination of warmth and comfort offered by these long johns is truly outstanding. The unique interlock knit construction provides impressive breathability, particularly for a substantial 250 g/m² weight of 100% Merino wool. Designed with gussets both in the rear and front, they enhance overall comfort and ensure a superior fit. The inclusion of an extra-wide, wool-lined waistband alongside full-flatlock seams effectively addresses common itchiness issues often associated with long underwear. While specifically engineered for cold weather, their balanced warmth and breathability make them adaptable even as temperatures moderately increase.
Despite their robust construction, making them one of the more durable natural fiber options we examined, all Merino wool garments demand a higher level of care than typical clothing. With regular wear between washes, the Classic Thermal long johns tend to lose shape, potentially leading to the temptation to use a dryer for shrinkage. However, avoid this! Proper care, including careful washing and primarily flat or line drying, is essential to maximize the lifespan of these and all Merino base layers. Although the laundering process might be slightly more involved, the exceptional thermoregulation capabilities justify the additional effort, especially for individuals active in very cold environments. If the specific laundry needs of wool seem inconvenient, consider a synthetic alternative such as the REI Co-op Midweight Bottoms.
Read more: Smartwool Classic Thermal Merino Bottom review
Close-up shot of a tester's legs wearing Smartwool Classic Thermal Merino Bottoms, showing the fitted yet comfortable design
These thick long johns are easy to put on, and wear somewhat fitted on our tester’s legs.
Best Synthetic Bang for the Buck
REI Co-op Midweight Bottoms
$55 at REI (before member cash back!)
OVERALL SCORE: 73
- Warmth 7.0
- Breathability 7.0
- Comfort and Fit 7.0
- Durability 9.0
- Drying Speed 7.0
- Layering Ability 7.0
Materials: 100% polyester | Weight: 7.4 oz (size Medium)
REASONS TO BUY
- Highly durable and able to withstand rigorous use
- Offers excellent performance at a budget-friendly price
- Features comfortable four-way stretch fabric for ease of movement
REASONS TO AVOID
- May not provide as much warmth for its weight compared to wool
Following a significant redesign, the REI Co-op Midweight Bottoms have become even more impressive as a top-value, incredibly robust, and practical choice in synthetic long johns. REI seems to have addressed previous criticisms, as these long johns now boast a significantly enhanced four-way stretch 100% polyester fabric that we highly appreciate. The exceptional durability and reliable warmth of the Midweight model remain, along with its generally understated design and cut—fitting snugly but not overly tight, suitable for a wide range of users and activities. This pair stands out as the warmest synthetic mid-layer we’ve tested, rivaling even some 200 g/m² 100% Merino wool long underwear options.
Since REI’s updates to the Midweight Bottoms, there are minimal drawbacks to note. This straightforward piece of gear performs effectively without unnecessary frills, focusing on reliable function over accolades. Its performance is hard to match, especially considering its affordable price. For those seeking a warmer layer, perhaps with enhanced softness and comfort, a wool option like the Smartwool Classic Thermal Merino Bottom would be more appropriate, reserving these for milder conditions.
Read more: REI Co-op Midweight Bottoms review
REI Co-op Midweight Bottoms fabric drying quickly, demonstrating their fast-drying synthetic properties
The synthetic fabric of the REI Co-op Midweight Bottoms dries faster than many wool bottoms in our tests.
Merino Wool on a Budget
Meriwool Merino 250 Bottom
Meriwool Merino 250 Bottom long johns, showcasing their classic design and merino wool texture
OVERALL SCORE: 67
- Warmth 8.0
- Breathability 6.0
- Comfort and Fit 7.0
- Durability 6.0
- Drying Speed 6.0
- Layering Ability 6.0
Materials: 100% Merino Wool | Weight: 7.9 oz (size Medium)
REASONS TO BUY
- Delivers good overall performance at an exceptional value
- Made with super warm 100% Merino wool for excellent insulation
- Available in a wide array of sizes to fit various body types
REASONS TO AVOID
- Construction may not be as comfortable as designs with more paneling
- Tends to run slightly smaller in size compared to average
The Meriwool Merino 250 Bottom makes 100% Merino Wool apparel accessible to a broader audience. We appreciate the straightforward, reliable construction and the exceptionally soft, comfortable 100% Merino wool fabric of these affordable long johns. High-quality features, like an extra-comfortable waistband and thoughtfully designed ankle cuffs, are surprisingly present given their very reasonable price. These are excellent thermal bottoms ideal for wearing when temperatures begin to drop significantly.
Beyond their overall warmth and the great value of obtaining 100% Merino wool bottoms at such an affordable price, these long johns are characterized by their understated effectiveness. They work efficiently and discreetly (underneath your outerwear) to keep you comfortably warm in cold conditions without needing excessive attention. It’s worth noting that a brief break-in period might be needed to fully soften the ultra-fine Merino wool. Therefore, if the Merino 250 Bottom feels slightly itchy upon initial wear, washing them before making a final judgment is recommended. For those prioritizing maximum comfort from the start, the Artilect Boulder 125, which blends wool with stretchy nylon, offers a softer feel.
Read more: Meriwool Merino 250 Bottom review
The Meriwool Merino 250 Bottoms offer a comfortable fit and are a great way to add warmth without spending too much.
Best Lightweight Long Underwear
Artilect Boulder 125
OVERALL SCORE: 74
- Warmth 5.0
- Breathability 10.0
- Comfort and Fit 8.0
- Durability 6.0
- Drying Speed 8.0
- Layering Ability 8.0
Materials: 85% Merino wool, 15% nylon | Weight: 4.3 oz (size Medium)
REASONS TO BUY
- Exceptionally breathable, perfect for high-output activities
- Ultralightweight design for minimal bulk and maximum mobility
- Made with a stretchy nylon/Merino wool blend for comfort and performance
REASONS TO AVOID
- Premium quality comes with a higher price tag
- Requires careful adherence to washing and drying instructions to maintain quality
The meticulously crafted Artilect Boulder 125 long johns utilize advanced composite materials, including the comfortable and warm 125 g/m² Nuyarn—a blend of 85% Merino and 15% nylon. These Best Long Johns also feature a complex panel construction with integrated perforations designed to release excess heat and moisture. This design ensures excellent thermoregulation during fast-paced activities in chilly conditions. Although intended to be worn under pants or tights, they also look stylish enough to wear alone when relaxing at home or in a camper van.
Aligning with its emphasis on speed and efficiency, the Boulder 125 is not an all-purpose option. It is best suited for milder weather conditions, and swapping to a warmer alternative is recommended for colder winter expeditions. The price reflects its luxurious quality, being higher than many other options, but the superior performance justifies the investment. These are the ideal long johns to ensure maximum comfort and lightness during outdoor adventures. For colder climates, consider the Smartwool Classic Thermal Merino Bottom instead.
Read more: Artilect Boulder 125 review
Artilect Boulder 125 long johns drying rapidly in a breeze, highlighting their quick-drying and breathable fabric
The Artilect Boulder 125 long johns are highly breathable and dry quickly, ideal for active use.
Best Midweight
Minus33 Kancamagus Midweight Merino Wool Bottoms
Minus33 Kancamagus Midweight Merino Wool Bottoms, showing their classic full-length design and merino wool texture
OVERALL SCORE: 73
- Warmth 9.0
- Breathability 7.0
- Comfort and Fit 7.0
- Durability 6.0
- Drying Speed 6.0
- Layering Ability 7.0
Materials: 100% Merino wool | Weight: 8.9 oz (size Medium)
REASONS TO BUY
- Made with plush 100% Merino wool for superior comfort and warmth
- Features secure ankle cuffs and a high waist for a snug fit
- Offers good value for high-quality merino wool
REASONS TO AVOID
- More prone to damage than synthetic options
- Longer drying times compared to synthetic fabrics
- May not be as breathable in warmer conditions
Midweight long johns are our preferred choice for cold days and nights—anything heavier can feel restrictive. A standout midweight option is the Minus33 Kancamagus Midweight Merino Wool Bottoms, which effectively combines 235 g/sm, 100% Merino wool with smooth, low-profile flatlock seams, providing a near-perfect body fit. We often choose these best long johns when anticipating cold weather, as they offer excellent thermoregulation in frigid environments. The soft, smooth fabric feels exceptionally comfortable against the skin and layers seamlessly under outer garments.
Like other 100% Merino wool bottoms, these require gentle care, particularly considering their direct skin contact. All Merino wool bottoms are susceptible to damage from rough surfaces, and the Kancamagus is no exception. This pair is also too warm for milder temperatures, making a lighter option more suitable for summer. The REI Co-op Merino 185 Bottoms are an excellent choice for warmer weather when some warmth is still needed.
Read more: Minus33 Kancamagus Midweight Merino Wool Bottoms review
The Minus33 Kancamagus Midweight Merino Wool Bottoms are ideal for cold alpine nights and bivy sack adventures.
Our Favorite 3/4 Length
Smartwool Intraknit Thermal Merino 3/4 Bottom
OVERALL SCORE: 72
- Warmth 7.0
- Breathability 7.0
- Comfort and Fit 7.0
- Durability 8.0
- Drying Speed 5.0
- Layering Ability 9.0
Materials: 54% Merino wool, 43% polyester, 2% elastane, 1% polyamide | Weight: 9.2 oz (size Medium)
REASONS TO BUY
- Seamless panels offer enhanced warmth, ventilation, and flexibility
- Features a nice, thick waistband for secure and comfortable wear
- 3/4 length design helps keep sock and boot areas less bulky
REASONS TO AVOID
- No fly design might be inconvenient for some users
- Athletic fit may not appeal to everyone
Our appreciation for Smartwool’s Intraknit technology is significant, which is a key reason why the Smartwool Intraknit Thermal Merino 3/4 Bottom is a top pick. The seamless panels strategically blend different fabrics to create long johns that are both warm and well-ventilated in specific zones. For instance, the gusseted crotch fabric promotes moisture evaporation, while the fabric around the knees enhances articulation. All of these features are integrated into a snug, athletic fit with a high waist supported by a substantial waistband.
What are the downsides? If a close, almost compression-like fit is not preferred, the Intraknit Thermal might not be ideal. The absence of a fly is also a deterrent for some. Additionally, the advanced technology increases the price. The variety of fabrics in the Intraknit construction also makes them slightly heavier than other options. For ultimate warmth, there are alternatives (including full-length versions of these), but for versatility and performance, these are outstanding. However, for those who prefer a comfortable four-way stretch at a lower cost, the REI Co-op Midweight Bottoms are an excellent alternative.
Read more: Smartwool Intraknit Thermal Merino 3/4 Bottom review
Smartwool Intraknit Thermal Merino 3/4 Bottoms being hand-washed under a waterfall, demonstrating their care requirements
While durable, the Smartwool Intraknit Thermal Merino 3/4 Bottoms benefit from hand washing and air drying.
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A group of people on a river trip, testing long underwear in a real-world setting
River trips provide excellent conditions for testing the performance of long underwear bottoms.
Why Trust GearLab
Our approach to testing men’s long underwear is comprehensive, using both lab-based and field testing methods. In controlled lab settings, we conduct repeatable tests to directly compare each pair of long johns. Durability is assessed through abrasion tests and multiple wash and dry cycles. Warmth and breathability are measured in climate-controlled environments to ensure standardized comparisons. Additionally, we evaluate these best long johns in real-world outdoor conditions, assessing their performance during activities like mountain hiking, fastpacking, and daily commutes in varying weather. We focus on practical aspects such as comfort, fit, and resilience under typical use.
Spin bikes in a gym are used to test warmth and breathability of long underwear in a controlled indoor environment.
Our long underwear testing evaluates six key metrics to provide a thorough review:
- Warmth (25% of total score)
- Breathability (20% of total score)
- Comfort and Fit (20% of total score)
- Durability (15% of total score)
- Drying Speed (10% of total score)
- Layering Ability (10% of total score)
Our lead expert in cold weather layering is Justin Simoni, a Colorado-based athlete and experienced backpacking guide. Justin specializes in long-distance, self-supported mountain challenges, requiring finely-tuned layering systems for varied elevations and conditions. He also consults with outdoor gear companies, bringing over a decade of expertise to gear assessment.
Justin collaborates with Aaron Rice, a ski patroller and snow scientist with deep knowledge of snow and cold weather environments. Aaron’s expertise in snow science and mountain activities enhances our testing and evaluations.
Field testing the Smartwool Merino 250 bottoms, currently known as the Classic Thermal, in snowy conditions.
Side-by-side comparison of long underwear waistbands, highlighting design differences for fit and comfortSide-by-side testing comparing waistbands, like the Ortovox 185 Rock’N’Wool’s wide band versus the Outdoor Research Alpine Onset’s thinner band.
Long underwear bottoms as a versatile addition to outdoor clothing for various activities
Long underwear bottoms are versatile and essential for a wide range of outdoor activities and conditions.
Our team of adventurers rigorously tests each pair of long underwear to determine the best options for different needs and conditions.
Analysis and Test Results
Long underwear, or base layer bottoms, are crucial for staying warm and regulating body temperature in cold weather. While often used primarily in winter, their versatility extends to backpacking pajamas, cold-weather running tights, or extra warmth under jeans. They are essential for activities like ice climbing and skiing, keeping you dry and comfortable by wicking away moisture and improving thermoregulation, enhancing your overall outdoor experience.
Person layering up with long underwear as the weather turns cold and snow begins to fall
Using long underwear as a base layer is essential when flurries start, providing crucial warmth and moisture management.
Our testing combines comprehensive lab work with practical field evaluations. Scores for each metric are compiled to determine an overall score relative to other products tested. It’s important to note that our reviews feature only top-performing layers; a lower score indicates relative performance within a selection of high-quality products, not overall product deficiency. By comparing these layers directly, we aim to highlight specific features to guide your purchase decisions for the best long johns.
What’s the Best Value?
High-performance long johns can be a significant investment. For frequent mountaineers, skiers, and winter campers, the cost is often justified by the performance benefits. However, for occasional use, more affordable options can still provide good quality.
Close-up of Ortovox wool long underwear, noting their high quality but potentially excessive features for basic needsHigh-end wool long underwear like Ortovox offers exceptional quality, but might be over-featured for everyday use cases.
Merino wool models generally cost more due to the material’s production expenses, although they offer the benefit of a natural product. Synthetic models are typically less expensive and often dry quickly, which is beneficial as temperatures rise. Despite production’s environmental impact, synthetics are often more durable and last longer, increasing their value over time.
For a warm and affordable option, the REI Co-op Midweight is recommended. For environmentally conscious buyers, the Patagonia Capilene Midweight Bottoms, made from 100% recycled polyester, are a good synthetic choice. For wool, the Meriwool Merino 250 Bottom offers excellent value, making wool more accessible.
Tag on Patagonia Capilene Midweights indicating "cool to cold" conditions, highlighting clear product informationSome base layers, like Patagonia Capilene Midweights, clearly indicate their ideal conditions, aiding consumer choice.
Warmth
Warmth is a primary factor when choosing long underwear. Effective warmth comes from trapping body heat within fabric fibers while wicking moisture away to keep you dry and comfortable. Thicker materials usually mean warmer layers, but fabric type and fit also affect breathability and comfort.
Base layer bottoms are versatile, and warmth needs vary. Consider how you’ll use them—from intense activities to casual wear in cold conditions. Are they for all-season use or mainly for winter? Will they be under technical hardshells or warmer ski pants? The warmest options aren’t always the most practical.
Warmth testing in a lab involves measuring heat retention during physical activity to assess insulation performance.
For versatile long johns across seasons, the REI Co-op Midweight Bottoms and Ortovox 185 Rock’N’Wool Short Pant are good midweight choices. For less intense warmth needs, lightweight options like the Outdoor Research Alpine Onset Bottoms, REI Co-op Merino 185 Bottoms, and Patagonia Capilene Midweight are suitable for summer backpacking or desert winter trips. For SkiMo training, the Artilect Boulder 125 prioritizes breathability over insulation.
For extreme cold, choose thick, 100% Merino wool bottoms, which retain the most heat. The Smartwool Classic Thermal Merino, Minus33 Kancamagus Midweight Merino Wool Bottoms, and Meriwool Merino 250 are excellent for maximum warmth in the best long johns category.
Magnified view of Smartwool Classic Thermal Merino Bottom’s knit, illustrating the dense structure of 100% merino wool.
Meriwool Merino 250 Bottom's 100% merino wool knit magnified to show fabric construction
Magnified view of Meriwool Merino 250 Bottom’s knit, displaying the texture and weave of 100% merino wool.
Magnified view of Minus33 Kancamagus Midweight Merino Wool Bottoms’ knit, highlighting the fine merino wool fibers.
Magnified views of 100% Merino Wool bottoms reveal their knit construction, showing different textures.
Breathability
Breathability is vital for base layer effectiveness in temperature regulation. It’s the fabric’s ability to move heat-induced moisture (sweat) from inside to outside, allowing evaporation and preventing overheating while staying dry. Better breathability keeps you warmer in cold conditions by preventing dampness.
Body temperature fluctuations are less intense in the lower body but still significant due to major muscle groups generating heat. Breathable long underwear is important for aerobic stop-start activities like backcountry skiing. Lighter fabric weights generally offer better breathability.
Hiking in long underwear, testing breathability on a warm day, highlighting the importance of ventilationTesting breathability of long underwear on a warm day to evaluate ventilation and moisture-wicking capabilities.
Most Merino wool layers offer superior moisture-wicking as a natural property. For highly breathable full Merino options, consider the Smartwool Classic Thermal and Ortovox 185 Rock’N’Wool as best long johns for breathability.
Person feeling free and comfortable in breathable long underwear, emphasizing comfort during activityBreathable long underwear enhances comfort and freedom during physical activities by managing moisture effectively.
While natural fibers excel at wicking, synthetics often dry faster. The Patagonia Capilene Midweight and REI Co-op Lightweight Bottoms are excellent synthetic options for moisture management. The Thermajohn Thermal Fleece Lined Set and WEERTI Thermal Fleece Lined Set, being thin, also provide good breathability.
REI Co-op Midweight Bottoms fabric drying quickly, demonstrating their fast-drying synthetic propertiesREI Co-op Lightweight Bottoms use perforated synthetic fabric to maximize breathability and air circulation during use.
The Artilect Boulder 125 leads in breathability, using an 85% Merino/15% nylon blend for a thin, breathable, and durable fabric. The Ortovox 185 Rock’N’Wool Short Pant balances breathability and warmth effectively with its soft 185 g/m² Merino fabric.
Artilect Boulder 125 long johns drying rapidly in a breeze, highlighting their quick-drying and breathable fabricArtilect long underwear excels in breathability, making it suitable for high-output activities where ventilation is key.
The Mons Royale Cascade Merino Flex Legging also scores well, with a thinner-than-expected 180 GSM Merino blend and an athletic fit that aids moisture transfer.
Mons Royale Cascade Merino leggings, thin and breathable with a comfortable, wide waistband for active wearMons Royale Cascade Merino leggings are thin, stretchy, and highly breathable, featuring a comfortable, wide waistband.
Comfort and Fit
Comfort is universally desired—soft, plush materials are key. Fit is subjective, varying by body type. We assess articulation, seam placement, cut, and design to identify potential issues for all users, but personal try-on is always recommended to ensure the best fit in long johns.
Factors for comfort and fit assessment include:
- Fabric feel against skin
- Fit tightness in areas like knees and cuffs
- Fabric stretch and mobility
- Waistband comfort and width
- Leg length and cuff fit
- Crotch depth and sag
- Seam type and stitch comfort
Direct comparison of various long underwear helps reveal nuances in fit and comfort across different models.
Comfort is generally high among top-tier products, so fit becomes a differentiator. For ultra-soft comfort, the Smartwool Classic Thermal Merino and its lighter version, the Classic All-Season, are excellent choices for best long johns in comfort.
Artilect Boulder 125s made of Nuyarn, combining merino wool comfort with synthetic stretch for enhanced fitArtilect Boulder 125s use Nuyarn merino wool spun around nylon, blending merino comfort with synthetic stretch.
Many long johns blend synthetics with wool for stretch and body-hugging fit, like the Smartwool Intraknit and Artilect Boulder 125. The Mons Royale Cascade Merino Flex Legging features an exceptionally wide, comfortable waistband that distributes pressure evenly.
Intraknit tech in Smartwool Intraknit Thermal Merino 3/4 Bottom enhancing stretch and movement, particularly at the kneeIntraknit technology in Smartwool Intraknit Thermal Merino 3/4 Bottoms improves stretch and mobility, especially in articulated areas like the knees.
Durability
Durability isn’t a primary focus for base layers, designed to be worn under other garments. Extra durability for double duty as running tights is a bonus, not a requirement.
Merino wool is traditionally delicate, but brands have improved its durability. Smartwool wraps Merino around nylon cores in the Intraknit Thermal Merino for enhanced strength. The Artilect Boulder 125 uses NuYarn similarly. The Outdoor Research Alpine Onset blends polyester and wool, aiming for combined benefits.
Durability being a key factor for long underwear on multi-day trips, requiring robust material and constructionLong underwear durability is crucial for multi-day trips, necessitating robust materials and construction for longevity.
While wool blends improve, synthetic long johns remain the most durable. The REI Co-op Midweight Bottoms score high in durability due to their tough, comfortable four-way stretch fabric. The Patagonia Capilene Midweight is also durable for its lighter weight.
Close-up shot of a tester's legs wearing Smartwool Classic Thermal Merino Bottoms, showing the fitted yet comfortable designREI Midweight Bottoms demonstrate excellent durability with abrasion-resistant synthetic fabric and a robust four-way stretch.
Drying Speed
Drying speed is important because many base layer materials shouldn’t be machine-dried. Wool shrinks and degrades in dryers. Even most synthetics and 100% Merino wool with elastane degrade with machine drying. Line drying or flat drying is recommended. Line drying speed also indicates how quickly bottoms dry when worn, related to breathability.
Lighter fabrics dry faster. The WEERTI Thermal Fleece Lined Set and Thermajohn Thermal Fleece Lined Set dry very quickly due to their lightweight synthetic fabrics. However, they may pill, so line drying is best.
Heavier bottoms can also dry surprisingly fast. The Icebreaker Merino 200 Oasis Bottoms dry quickly for their weight, as does the 3/4 length Ortovox 185 Rock’N’Wool Short Pant. The Patagonia Capilene Midweight, our fastest synthetic, and the lightweight Artilect Boulder 125 and Mons Royale Cascade Merino Flex Legging also dry quickly.
Icebreaker Oasis 200 long underwear drying impressively fast for their weight, highlighting efficient moisture managementIcebreaker Oasis 200 long underwear demonstrate impressively fast drying times, especially considering their fabric weight.
Layering Ability
Good long johns should layer well within a clothing system. We assess features like low-profile flatlock seams to prevent chafing, waistbands that stay in place, and leg cuffs that stay down. A front fly adds convenience, while a fly-less design can allow for wearing without additional undergarments. A tighter fit also helps outer layers slide on easily.
The Smartwool Intraknit Thermal has a tight, compression-like fit, and the 3/4 length prevents sock bunching. The Outdoor Research Alpine Onset Bottoms and REI Co-op Merino 185 Bottoms also fit close to the skin, facilitating easy layering.
Versatile long underwear like Outdoor Research Alpine Onset bottoms, ideal for layering in various outdoor adventuresVersatile long underwear bottoms, such as Outdoor Research Alpine Onset, enhance layering for diverse outdoor activities.
Conclusion
Long underwear bottoms are essential for extending your outdoor season into colder months. When choosing your next pair, consider your temperature preferences and planned activities. Our tests across various climates identified options suitable for warmer and colder seasons, emphasizing that the right choice significantly impacts comfort and performance. From skiing to backpacking to everyday warmth, these versatile bottoms will keep you warm and dry in any activity or situation.
Long underwear bottoms as a versatile addition to outdoor clothing for various activities
Where will your next pair of best long johns take you in your cold-weather explorations and adventures?
